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 $59.72   6.234%   $63.4429   $63.44   $63.45   $63.40  
  Purchase #2 $216.48   9.315%   $236.6451   $236.65   $236.65   $236.60  
  Purchase #3 $35.88   10.194%   $39.5376   $39.54   $39.55   $39.50  
  Purchase #4 $233.63   7.448%   $251.0308   $251.03   $251.05   $251.00  
  Purchase #5 $140.45   11.176%   $156.1467   $156.15   $156.15   $156.10  
  Purchase #6 $147.49   13.500%   $167.4012   $167.40   $167.40   $167.40  
  Purchase #7 $116.33   3.324%   $120.1968   $120.20   $120.20   $120.20  
  7 purchase totals = $949.98       $1,034.4011   $1,034.41   $1,034.45   $1,034.20