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 $63.62   5.785%   $67.3004   $67.30   $67.30   $67.30  
  Purchase #2 $171.72   7.618%   $184.8016   $184.80   $184.80   $184.80  
  Purchase #3 $49.47   9.774%   $54.3052   $54.31   $54.30   $54.30  
  Purchase #4 $235.59   9.825%   $258.7367   $258.74   $258.75   $258.70  
  Purchase #5 $95.56   6.516%   $101.7867   $101.79   $101.80   $101.80  
  Purchase #6 $29.48   13.655%   $33.5055   $33.51   $33.50   $33.50  
  Purchase #7 $211.45   8.128%   $228.6367   $228.64   $228.65   $228.60  
  7 purchase totals = $856.89       $929.0728   $929.09   $929.10   $929.00