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 $148.79   6.196%   $158.009   $158.01   $158.00   $158.00  
  Purchase #2 $58.87   13.775%   $66.9793   $66.98   $67.00   $67.00  
  Purchase #3 $91.31   12.415%   $102.6461   $102.65   $102.65   $102.60  
  Purchase #4 $126.73   5.640%   $133.8776   $133.88   $133.90   $133.90  
  Purchase #5 $33.68   11.544%   $37.568   $37.57   $37.55   $37.60  
  Purchase #6 $85.42   13.419%   $96.8825   $96.88   $96.90   $96.90  
  Purchase #7 $121.56   12.577%   $136.8486   $136.85   $136.85   $136.80  
  7 purchase totals = $666.36       $732.8111   $732.82   $732.85   $732.80