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 $101.65   11.689%   $113.5319   $113.53   $113.55   $113.50  
  Purchase #2 $20.79   12.848%   $23.4611   $23.46   $23.45   $23.50  
  Purchase #3 $244.87   8.345%   $265.3044   $265.30   $265.30   $265.30  
  Purchase #4 $176.76   4.415%   $184.564   $184.56   $184.55   $184.60  
  Purchase #5 $241.53   7.294%   $259.1472   $259.15   $259.15   $259.10  
  Purchase #6 $89.41   13.617%   $101.585   $101.59   $101.60   $101.60  
  Purchase #7 $126.84   3.744%   $131.5889   $131.59   $131.60   $131.60  
  7 purchase totals = $1,001.85       $1,079.1825   $1,079.18   $1,079.20   $1,079.20