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 $77.64   12.390%   $87.2596   $87.26   $87.25   $87.30  
  Purchase #2 $52.52   9.373%   $57.4427   $57.44   $57.45   $57.40  
  Purchase #3 $250.97   9.420%   $274.6114   $274.61   $274.60   $274.60  
  Purchase #4 $248.77   7.623%   $267.7337   $267.73   $267.75   $267.70  
  Purchase #5 $197.47   10.148%   $217.5093   $217.51   $217.50   $217.50  
  Purchase #6 $209.74   7.658%   $225.8019   $225.80   $225.80   $225.80  
  Purchase #7 $210.95   10.383%   $232.8529   $232.85   $232.85   $232.90  
  7 purchase totals = $1,248.06       $1,363.2115   $1,363.20   $1,363.20   $1,363.20