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 $86.35   7.110%   $92.4895   $92.49   $92.50   $92.50  
  Purchase #2 $66.87   11.441%   $74.5206   $74.52   $74.50   $74.50  
  Purchase #3 $51.38   4.550%   $53.7178   $53.72   $53.70   $53.70  
  Purchase #4 $158.33   13.427%   $179.589   $179.59   $179.60   $179.60  
  Purchase #5 $207.29   13.731%   $235.753   $235.75   $235.75   $235.80  
  Purchase #6 $104.25   13.831%   $118.6688   $118.67   $118.65   $118.70  
  Purchase #7 $87.67   5.747%   $92.7084   $92.71   $92.70   $92.70  
  7 purchase totals = $762.14       $847.4471   $847.45   $847.40   $847.50