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 $69.60   6.677%   $74.2472   $74.25   $74.25   $74.20  
  Purchase #2 $211.42   7.192%   $226.6253   $226.63   $226.65   $226.60  
  Purchase #3 $21.62   12.412%   $24.3035   $24.30   $24.30   $24.30  
  Purchase #4 $32.29   10.403%   $35.6491   $35.65   $35.65   $35.60  
  Purchase #5 $83.30   13.541%   $94.5797   $94.58   $94.60   $94.60  
  Purchase #6 $206.72   9.622%   $226.6106   $226.61   $226.60   $226.60  
  Purchase #7 $22.67   7.241%   $24.3115   $24.31   $24.30   $24.30  
  7 purchase totals = $647.62       $706.3269   $706.33   $706.35   $706.20