Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $244.52   9.324%   $267.319   $267.32   $267.30   $267.30  
  Purchase #2 $118.37   9.862%   $130.0436   $130.04   $130.05   $130.00  
  Purchase #3 $126.41   7.482%   $135.868   $135.87   $135.85   $135.90  
  Purchase #4 $127.30   3.829%   $132.1743   $132.17   $132.15   $132.20  
  Purchase #5 $110.41   10.138%   $121.6034   $121.60   $121.60   $121.60  
  Purchase #6 $179.74   4.735%   $188.2507   $188.25   $188.25   $188.30  
  Purchase #7 $211.50   5.667%   $223.4857   $223.49   $223.50   $223.50  
  7 purchase totals = $1,118.25       $1,198.7447   $1,198.74   $1,198.70   $1,198.80