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 $85.29   11.145%   $94.7956   $94.80   $94.80   $94.80  
  Purchase #2 $165.31   10.703%   $183.0031   $183.00   $183.00   $183.00  
  Purchase #3 $215.35   7.790%   $232.1258   $232.13   $232.15   $232.10  
  Purchase #4 $9.39   4.264%   $9.7904   $9.79   $9.80   $9.80  
  Purchase #5 $127.31   9.151%   $138.9601   $138.96   $138.95   $139.00  
  Purchase #6 $96.28   11.695%   $107.5399   $107.54   $107.55   $107.50  
  Purchase #7 $93.35   9.581%   $102.2939   $102.29   $102.30   $102.30  
  7 purchase totals = $792.28       $868.5088   $868.51   $868.55   $868.50