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 $61.87   10.466%   $68.3453   $68.35   $68.35   $68.30  
  Purchase #2 $80.95   11.695%   $90.4171   $90.42   $90.40   $90.40  
  Purchase #3 $149.59   13.507%   $169.7951   $169.80   $169.80   $169.80  
  Purchase #4 $53.42   5.803%   $56.52   $56.52   $56.50   $56.50  
  Purchase #5 $160.63   10.492%   $177.4833   $177.48   $177.50   $177.50  
  Purchase #6 $63.35   13.624%   $71.9808   $71.98   $72.00   $72.00  
  Purchase #7 $38.39   8.866%   $41.7937   $41.79   $41.80   $41.80  
  7 purchase totals = $608.20       $676.3353   $676.34   $676.35   $676.30