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 $67.44   11.177%   $74.9778   $74.98   $75.00   $75.00  
  Purchase #2 $186.34   6.211%   $197.9136   $197.91   $197.90   $197.90  
  Purchase #3 $219.32   5.681%   $231.7796   $231.78   $231.80   $231.80  
  Purchase #4 $57.50   9.184%   $62.7808   $62.78   $62.80   $62.80  
  Purchase #5 $136.96   4.859%   $143.6149   $143.61   $143.60   $143.60  
  Purchase #6 $165.70   4.743%   $173.5592   $173.56   $173.55   $173.60  
  Purchase #7 $235.44   12.607%   $265.1219   $265.12   $265.10   $265.10  
  7 purchase totals = $1,068.70       $1,149.7478   $1,149.74   $1,149.75   $1,149.80