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 $44.59   3.499%   $46.1502   $46.15   $46.15   $46.20  
  Purchase #2 $64.57   11.421%   $71.9445   $71.94   $71.95   $71.90  
  Purchase #3 $131.73   10.756%   $145.8989   $145.90   $145.90   $145.90  
  Purchase #4 $120.62   9.870%   $132.5252   $132.53   $132.55   $132.50  
  Purchase #5 $174.35   11.255%   $193.9731   $193.97   $193.95   $194.00  
  Purchase #6 $101.52   9.748%   $111.4162   $111.42   $111.40   $111.40  
  Purchase #7 $202.55   7.193%   $217.1194   $217.12   $217.10   $217.10  
  7 purchase totals = $839.93       $919.0275   $919.03   $919.00   $919.00