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 $60.50   12.731%   $68.2023   $68.20   $68.20   $68.20  
  Purchase #2 $68.68   8.702%   $74.6565   $74.66   $74.65   $74.70  
  Purchase #3 $161.92   3.737%   $167.971   $167.97   $167.95   $168.00  
  Purchase #4 $204.51   10.217%   $225.4048   $225.40   $225.40   $225.40  
  Purchase #5 $105.30   3.821%   $109.3235   $109.32   $109.30   $109.30  
  Purchase #6 $153.81   5.726%   $162.6172   $162.62   $162.60   $162.60  
  Purchase #7 $154.91   5.387%   $163.255   $163.26   $163.25   $163.30  
  7 purchase totals = $909.63       $971.4303   $971.43   $971.35   $971.50