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 $245.62   5.839%   $259.9618   $259.96   $259.95   $260.00  
  Purchase #2 $92.27   4.375%   $96.3068   $96.31   $96.30   $96.30  
  Purchase #3 $137.61   11.196%   $153.0168   $153.02   $153.00   $153.00  
  Purchase #4 $151.43   6.108%   $160.6793   $160.68   $160.70   $160.70  
  Purchase #5 $94.54   8.757%   $102.8189   $102.82   $102.80   $102.80  
  Purchase #6 $22.92   7.324%   $24.5987   $24.60   $24.60   $24.60  
  Purchase #7 $182.46   11.689%   $203.7877   $203.79   $203.80   $203.80  
  7 purchase totals = $926.85       $1,001.1700   $1,001.18   $1,001.15   $1,001.20