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 $62.56   7.518%   $67.2633   $67.26   $67.25   $67.30  
  Purchase #2 $221.52   6.578%   $236.0916   $236.09   $236.10   $236.10  
  Purchase #3 $138.42   8.497%   $150.1815   $150.18   $150.20   $150.20  
  Purchase #4 $238.68   13.490%   $270.8779   $270.88   $270.90   $270.90  
  Purchase #5 $36.91   13.383%   $41.8497   $41.85   $41.85   $41.80  
  Purchase #6 $235.92   4.370%   $246.2297   $246.23   $246.25   $246.20  
  Purchase #7 $16.52   5.308%   $17.3969   $17.40   $17.40   $17.40  
  7 purchase totals = $950.53       $1,029.8906   $1,029.89   $1,029.95   $1,029.90