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 $60.67   7.273%   $65.0825   $65.08   $65.10   $65.10  
  Purchase #2 $218.55   11.713%   $244.1488   $244.15   $244.15   $244.10  
  Purchase #3 $16.59   12.316%   $18.6332   $18.63   $18.65   $18.60  
  Purchase #4 $56.32   3.487%   $58.2839   $58.28   $58.30   $58.30  
  Purchase #5 $67.33   4.564%   $70.4029   $70.40   $70.40   $70.40  
  Purchase #6 $106.59   13.206%   $120.6663   $120.67   $120.65   $120.70  
  Purchase #7 $159.50   8.780%   $173.5041   $173.50   $173.50   $173.50  
  7 purchase totals = $685.55       $750.7217   $750.71   $750.75   $750.70