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 $142.86   6.208%   $151.7287   $151.73   $151.75   $151.70  
  Purchase #2 $170.81   11.817%   $190.9946   $190.99   $191.00   $191.00  
  Purchase #3 $43.95   11.764%   $49.1203   $49.12   $49.10   $49.10  
  Purchase #4 $191.38   3.240%   $197.5807   $197.58   $197.60   $197.60  
  Purchase #5 $178.45   5.640%   $188.5146   $188.51   $188.50   $188.50  
  Purchase #6 $56.88   12.690%   $64.0981   $64.10   $64.10   $64.10  
  Purchase #7 $190.26   6.635%   $202.8838   $202.88   $202.90   $202.90  
  7 purchase totals = $974.59       $1,044.9208   $1,044.91   $1,044.95   $1,044.90