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 $45.35   5.825%   $47.9916   $47.99   $48.00   $48.00  
  Purchase #2 $146.40   12.843%   $165.2022   $165.20   $165.20   $165.20  
  Purchase #3 $187.99   10.426%   $207.5898   $207.59   $207.60   $207.60  
  Purchase #4 $231.52   11.691%   $258.587   $258.59   $258.60   $258.60  
  Purchase #5 $158.70   6.438%   $168.9171   $168.92   $168.90   $168.90  
  Purchase #6 $30.67   11.277%   $34.1287   $34.13   $34.15   $34.10  
  Purchase #7 $224.66   8.412%   $243.5584   $243.56   $243.55   $243.60  
  7 purchase totals = $1,025.29       $1,125.9748   $1,125.98   $1,126.00   $1,126.00