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 $38.55   12.446%   $43.3479   $43.35   $43.35   $43.30  
  Purchase #2 $138.75   8.180%   $150.0998   $150.10   $150.10   $150.10  
  Purchase #3 $112.47   6.327%   $119.586   $119.59   $119.60   $119.60  
  Purchase #4 $140.88   7.865%   $151.9602   $151.96   $151.95   $152.00  
  Purchase #5 $48.33   7.467%   $51.9388   $51.94   $51.95   $51.90  
  Purchase #6 $205.30   7.129%   $219.9358   $219.94   $219.95   $219.90  
  Purchase #7 $192.91   7.412%   $207.2085   $207.21   $207.20   $207.20  
  7 purchase totals = $877.19       $944.0770   $944.09   $944.10   $944.00