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 $66.54   5.251%   $70.034   $70.03   $70.05   $70.00  
  Purchase #2 $96.98   12.310%   $108.9182   $108.92   $108.90   $108.90  
  Purchase #3 $14.81   12.125%   $16.6057   $16.61   $16.60   $16.60  
  Purchase #4 $168.41   3.373%   $174.0905   $174.09   $174.10   $174.10  
  Purchase #5 $192.95   6.254%   $205.0171   $205.02   $205.00   $205.00  
  Purchase #6 $100.92   5.435%   $106.405   $106.41   $106.40   $106.40  
  Purchase #7 $151.63   9.610%   $166.2016   $166.20   $166.20   $166.20  
  7 purchase totals = $792.24       $847.2721   $847.28   $847.25   $847.20