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 $43.86   5.523%   $46.2824   $46.28   $46.30   $46.30  
  Purchase #2 $182.70   10.187%   $201.3116   $201.31   $201.30   $201.30  
  Purchase #3 $110.53   9.643%   $121.1884   $121.19   $121.20   $121.20  
  Purchase #4 $116.84   5.327%   $123.0641   $123.06   $123.05   $123.10  
  Purchase #5 $223.59   10.452%   $246.9596   $246.96   $246.95   $247.00  
  Purchase #6 $15.55   9.460%   $17.021   $17.02   $17.00   $17.00  
  Purchase #7 $78.68   7.743%   $84.7722   $84.77   $84.75   $84.80  
  7 purchase totals = $771.75       $840.5993   $840.59   $840.55   $840.70