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 $94.82   12.611%   $106.7778   $106.78   $106.80   $106.80  
  Purchase #2 $27.71   3.502%   $28.6804   $28.68   $28.70   $28.70  
  Purchase #3 $158.52   4.689%   $165.953   $165.95   $165.95   $166.00  
  Purchase #4 $18.62   5.782%   $19.6966   $19.70   $19.70   $19.70  
  Purchase #5 $210.66   5.178%   $221.568   $221.57   $221.55   $221.60  
  Purchase #6 $15.41   5.738%   $16.2942   $16.29   $16.30   $16.30  
  Purchase #7 $169.83   3.640%   $176.0118   $176.01   $176.00   $176.00  
  7 purchase totals = $695.57       $734.9818   $734.98   $735.00   $735.10