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 $202.32   10.211%   $222.9789   $222.98   $223.00   $223.00  
  Purchase #2 $76.77   11.114%   $85.3022   $85.30   $85.30   $85.30  
  Purchase #3 $228.35   5.791%   $241.5737   $241.57   $241.55   $241.60  
  Purchase #4 $246.53   4.481%   $257.577   $257.58   $257.60   $257.60  
  Purchase #5 $6.58   11.264%   $7.3212   $7.32   $7.30   $7.30  
  Purchase #6 $104.95   9.697%   $115.127   $115.13   $115.15   $115.10  
  Purchase #7 $61.82   10.103%   $68.0657   $68.07   $68.05   $68.10  
  7 purchase totals = $927.32       $997.9457   $997.95   $997.95   $998.00