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 $96.32   8.766%   $104.7634   $104.76   $104.75   $104.80  
  Purchase #2 $183.28   10.454%   $202.4401   $202.44   $202.45   $202.40  
  Purchase #3 $74.73   7.386%   $80.2496   $80.25   $80.25   $80.20  
  Purchase #4 $247.57   12.867%   $279.4248   $279.42   $279.40   $279.40  
  Purchase #5 $217.45   8.383%   $235.6788   $235.68   $235.70   $235.70  
  Purchase #6 $226.38   8.873%   $246.4667   $246.47   $246.45   $246.50  
  Purchase #7 $165.49   7.641%   $178.1351   $178.14   $178.15   $178.10  
  7 purchase totals = $1,211.22       $1,327.1585   $1,327.16   $1,327.15   $1,327.10