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 $231.81   10.729%   $256.6809   $256.68   $256.70   $256.70  
  Purchase #2 $102.52   5.349%   $108.0038   $108.00   $108.00   $108.00  
  Purchase #3 $84.50   11.491%   $94.2099   $94.21   $94.20   $94.20  
  Purchase #4 $173.81   10.719%   $192.4407   $192.44   $192.45   $192.40  
  Purchase #5 $58.82   7.103%   $62.998   $63.00   $63.00   $63.00  
  Purchase #6 $225.66   5.526%   $238.13   $238.13   $238.15   $238.10  
  Purchase #7 $66.71   11.557%   $74.4197   $74.42   $74.40   $74.40  
  7 purchase totals = $943.83       $1,026.8830   $1,026.88   $1,026.90   $1,026.80