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 $210.86   7.652%   $226.995   $227.00   $227.00   $227.00  
  Purchase #2 $165.66   13.174%   $187.484   $187.48   $187.50   $187.50  
  Purchase #3 $226.43   10.807%   $250.9003   $250.90   $250.90   $250.90  
  Purchase #4 $88.96   6.196%   $94.472   $94.47   $94.45   $94.50  
  Purchase #5 $153.76   7.828%   $165.7963   $165.80   $165.80   $165.80  
  Purchase #6 $210.82   6.140%   $223.7643   $223.76   $223.75   $223.80  
  Purchase #7 $135.38   3.494%   $140.1102   $140.11   $140.10   $140.10  
  7 purchase totals = $1,191.87       $1,289.5221   $1,289.52   $1,289.50   $1,289.60