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 $34.66   6.149%   $36.7912   $36.79   $36.80   $36.80  
  Purchase #2 $234.73   6.776%   $250.6353   $250.64   $250.65   $250.60  
  Purchase #3 $30.25   7.807%   $32.6116   $32.61   $32.60   $32.60  
  Purchase #4 $167.72   5.817%   $177.4763   $177.48   $177.50   $177.50  
  Purchase #5 $59.48   12.705%   $67.0369   $67.04   $67.05   $67.00  
  Purchase #6 $231.89   6.237%   $246.353   $246.35   $246.35   $246.40  
  Purchase #7 $161.29   6.140%   $171.1932   $171.19   $171.20   $171.20  
  7 purchase totals = $920.02       $982.0975   $982.10   $982.15   $982.10