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 $173.50   13.840%   $197.5124   $197.51   $197.50   $197.50  
  Purchase #2 $112.47   12.136%   $126.1194   $126.12   $126.10   $126.10  
  Purchase #3 $194.92   12.872%   $220.0101   $220.01   $220.00   $220.00  
  Purchase #4 $75.29   7.155%   $80.677   $80.68   $80.70   $80.70  
  Purchase #5 $149.90   10.453%   $165.569   $165.57   $165.55   $165.60  
  Purchase #6 $173.94   7.465%   $186.9246   $186.92   $186.90   $186.90  
  Purchase #7 $18.87   3.567%   $19.5431   $19.54   $19.55   $19.50  
  7 purchase totals = $898.89       $996.3556   $996.35   $996.30   $996.30