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 $219.71   6.411%   $233.7956   $233.80   $233.80   $233.80  
  Purchase #2 $169.79   7.501%   $182.5259   $182.53   $182.55   $182.50  
  Purchase #3 $80.72   10.183%   $88.9397   $88.94   $88.95   $88.90  
  Purchase #4 $62.80   6.261%   $66.7319   $66.73   $66.75   $66.70  
  Purchase #5 $157.43   7.168%   $168.7146   $168.71   $168.70   $168.70  
  Purchase #6 $57.93   8.736%   $62.9908   $62.99   $63.00   $63.00  
  Purchase #7 $186.77   5.695%   $197.4066   $197.41   $197.40   $197.40  
  7 purchase totals = $935.15       $1,001.1051   $1,001.11   $1,001.15   $1,001.00