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 $154.30   13.391%   $174.9623   $174.96   $174.95   $175.00  
  Purchase #2 $111.31   10.691%   $123.2102   $123.21   $123.20   $123.20  
  Purchase #3 $195.55   13.411%   $221.7752   $221.78   $221.80   $221.80  
  Purchase #4 $25.96   8.638%   $28.2024   $28.20   $28.20   $28.20  
  Purchase #5 $213.37   7.625%   $229.6395   $229.64   $229.65   $229.60  
  Purchase #6 $193.70   12.774%   $218.4432   $218.44   $218.45   $218.40  
  Purchase #7 $97.97   7.285%   $105.1071   $105.11   $105.10   $105.10  
  7 purchase totals = $992.16       $1,101.3399   $1,101.34   $1,101.35   $1,101.30