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 $178.59   12.548%   $200.9995   $201.00   $201.00   $201.00  
  Purchase #2 $180.78   12.844%   $203.9994   $204.00   $204.00   $204.00  
  Purchase #3 $234.90   11.585%   $262.1132   $262.11   $262.10   $262.10  
  Purchase #4 $5.86   6.813%   $6.2592   $6.26   $6.25   $6.30  
  Purchase #5 $59.74   8.303%   $64.7002   $64.70   $64.70   $64.70  
  Purchase #6 $147.28   13.765%   $167.5531   $167.55   $167.55   $167.60  
  Purchase #7 $24.32   4.348%   $25.3774   $25.38   $25.40   $25.40  
  7 purchase totals = $831.47       $931.0020   $931.00   $931.00   $931.10