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 $62.68   7.681%   $67.4945   $67.49   $67.50   $67.50  
  Purchase #2 $210.74   10.392%   $232.6401   $232.64   $232.65   $232.60  
  Purchase #3 $172.99   11.828%   $193.4513   $193.45   $193.45   $193.50  
  Purchase #4 $87.82   7.476%   $94.3854   $94.39   $94.40   $94.40  
  Purchase #5 $62.43   7.220%   $66.9374   $66.94   $66.95   $66.90  
  Purchase #6 $249.45   3.554%   $258.3155   $258.32   $258.30   $258.30  
  Purchase #7 $58.39   7.150%   $62.5649   $62.56   $62.55   $62.60  
  7 purchase totals = $904.50       $975.7891   $975.79   $975.80   $975.80