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 $48.68   9.265%   $53.1902   $53.19   $53.20   $53.20  
  Purchase #2 $87.84   4.189%   $91.5196   $91.52   $91.50   $91.50  
  Purchase #3 $133.51   3.139%   $137.7009   $137.70   $137.70   $137.70  
  Purchase #4 $153.56   6.849%   $164.0773   $164.08   $164.10   $164.10  
  Purchase #5 $97.58   10.615%   $107.9381   $107.94   $107.95   $107.90  
  Purchase #6 $242.61   11.372%   $270.1996   $270.20   $270.20   $270.20  
  Purchase #7 $98.49   5.755%   $104.1581   $104.16   $104.15   $104.20  
  7 purchase totals = $862.27       $928.7838   $928.79   $928.80   $928.80