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 $83.35   11.241%   $92.7194   $92.72   $92.70   $92.70  
  Purchase #2 $48.55   6.626%   $51.7669   $51.77   $51.75   $51.80  
  Purchase #3 $160.99   12.288%   $180.7725   $180.77   $180.75   $180.80  
  Purchase #4 $150.63   3.709%   $156.2169   $156.22   $156.20   $156.20  
  Purchase #5 $24.33   4.731%   $25.4811   $25.48   $25.50   $25.50  
  Purchase #6 $134.80   6.547%   $143.6254   $143.63   $143.65   $143.60  
  Purchase #7 $92.74   10.458%   $102.4387   $102.44   $102.45   $102.40  
  7 purchase totals = $695.39       $753.0209   $753.03   $753.00   $753.00