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 $59.89   5.518%   $63.1947   $63.19   $63.20   $63.20  
  Purchase #2 $33.79   4.214%   $35.2139   $35.21   $35.20   $35.20  
  Purchase #3 $28.43   9.202%   $31.0461   $31.05   $31.05   $31.00  
  Purchase #4 $170.33   11.835%   $190.4886   $190.49   $190.50   $190.50  
  Purchase #5 $155.53   12.236%   $174.5607   $174.56   $174.55   $174.60  
  Purchase #6 $204.53   7.331%   $219.5241   $219.52   $219.50   $219.50  
  Purchase #7 $36.40   5.755%   $38.4948   $38.49   $38.50   $38.50  
  7 purchase totals = $688.90       $752.5229   $752.51   $752.50   $752.50