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 $59.66   13.427%   $67.6705   $67.67   $67.65   $67.70  
  Purchase #2 $177.54   12.408%   $199.5692   $199.57   $199.55   $199.60  
  Purchase #3 $170.73   3.697%   $177.0419   $177.04   $177.05   $177.00  
  Purchase #4 $92.71   10.459%   $102.4065   $102.41   $102.40   $102.40  
  Purchase #5 $227.35   3.451%   $235.1958   $235.20   $235.20   $235.20  
  Purchase #6 $28.40   9.814%   $31.1872   $31.19   $31.20   $31.20  
  Purchase #7 $196.87   11.572%   $219.6518   $219.65   $219.65   $219.70  
  7 purchase totals = $953.26       $1,032.7229   $1,032.73   $1,032.70   $1,032.80