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 $80.87   13.572%   $91.8457   $91.85   $91.85   $91.80  
  Purchase #2 $228.46   3.385%   $236.1934   $236.19   $236.20   $236.20  
  Purchase #3 $247.49   13.222%   $280.2131   $280.21   $280.20   $280.20  
  Purchase #4 $125.72   6.207%   $133.5234   $133.52   $133.50   $133.50  
  Purchase #5 $168.35   4.771%   $176.382   $176.38   $176.40   $176.40  
  Purchase #6 $218.68   12.616%   $246.2687   $246.27   $246.25   $246.30  
  Purchase #7 $96.73   5.625%   $102.1711   $102.17   $102.15   $102.20  
  7 purchase totals = $1,166.30       $1,266.5974   $1,266.59   $1,266.55   $1,266.60