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 $187.69   9.661%   $205.8227   $205.82   $205.80   $205.80  
  Purchase #2 $53.86   3.690%   $55.8474   $55.85   $55.85   $55.80  
  Purchase #3 $225.33   5.851%   $238.5141   $238.51   $238.50   $238.50  
  Purchase #4 $81.55   11.803%   $91.1753   $91.18   $91.20   $91.20  
  Purchase #5 $197.35   5.252%   $207.7148   $207.71   $207.70   $207.70  
  Purchase #6 $203.61   4.398%   $212.5648   $212.56   $212.55   $212.60  
  Purchase #7 $11.31   7.537%   $12.1624   $12.16   $12.15   $12.20  
  7 purchase totals = $960.70       $1,023.8015   $1,023.79   $1,023.75   $1,023.80