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 $197.60   7.299%   $212.0228   $212.02   $212.00   $212.00  
  Purchase #2 $245.32   10.480%   $271.0295   $271.03   $271.05   $271.00  
  Purchase #3 $197.86   3.483%   $204.7515   $204.75   $204.75   $204.80  
  Purchase #4 $58.43   4.329%   $60.9594   $60.96   $60.95   $61.00  
  Purchase #5 $35.61   8.633%   $38.6842   $38.68   $38.70   $38.70  
  Purchase #6 $238.26   12.168%   $267.2515   $267.25   $267.25   $267.30  
  Purchase #7 $23.93   8.645%   $25.9987   $26.00   $26.00   $26.00  
  7 purchase totals = $997.01       $1,080.6976   $1,080.69   $1,080.70   $1,080.80