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 $65.44   11.793%   $73.1573   $73.16   $73.15   $73.20  
  Purchase #2 $141.69   5.866%   $150.0015   $150.00   $150.00   $150.00  
  Purchase #3 $108.60   3.435%   $112.3304   $112.33   $112.35   $112.30  
  Purchase #4 $204.61   10.721%   $226.5462   $226.55   $226.55   $226.50  
  Purchase #5 $81.29   4.566%   $85.0017   $85.00   $85.00   $85.00  
  Purchase #6 $94.39   13.282%   $106.9269   $106.93   $106.95   $106.90  
  Purchase #7 $127.41   10.632%   $140.9562   $140.96   $140.95   $141.00  
  7 purchase totals = $823.43       $894.9202   $894.93   $894.95   $894.90