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 $224.28   5.347%   $236.2723   $236.27   $236.25   $236.30  
  Purchase #2 $206.43   3.154%   $212.9408   $212.94   $212.95   $212.90  
  Purchase #3 $33.28   8.600%   $36.1421   $36.14   $36.15   $36.10  
  Purchase #4 $91.46   3.278%   $94.4581   $94.46   $94.45   $94.50  
  Purchase #5 $194.50   5.382%   $204.968   $204.97   $204.95   $205.00  
  Purchase #6 $167.52   10.712%   $185.4647   $185.46   $185.45   $185.50  
  Purchase #7 $6.29   5.112%   $6.6115   $6.61   $6.60   $6.60  
  7 purchase totals = $923.76       $976.8575   $976.85   $976.80   $976.90