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 $30.62   8.623%   $33.2604   $33.26   $33.25   $33.30  
  Purchase #2 $104.67   13.743%   $119.0548   $119.05   $119.05   $119.10  
  Purchase #3 $36.36   8.296%   $39.3764   $39.38   $39.40   $39.40  
  Purchase #4 $216.67   13.544%   $246.0158   $246.02   $246.00   $246.00  
  Purchase #5 $189.47   9.459%   $207.392   $207.39   $207.40   $207.40  
  Purchase #6 $185.78   9.370%   $203.1876   $203.19   $203.20   $203.20  
  Purchase #7 $204.93   11.639%   $228.7818   $228.78   $228.80   $228.80  
  7 purchase totals = $968.50       $1,077.0688   $1,077.07   $1,077.10   $1,077.20