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 $220.35   9.709%   $241.7438   $241.74   $241.75   $241.70  
  Purchase #2 $148.76   12.622%   $167.5365   $167.54   $167.55   $167.50  
  Purchase #3 $225.36   9.649%   $247.105   $247.11   $247.10   $247.10  
  Purchase #4 $91.72   4.728%   $96.0565   $96.06   $96.05   $96.10  
  Purchase #5 $160.39   10.667%   $177.4988   $177.50   $177.50   $177.50  
  Purchase #6 $168.28   11.638%   $187.8644   $187.86   $187.85   $187.90  
  Purchase #7 $146.59   9.537%   $160.5703   $160.57   $160.55   $160.60  
  7 purchase totals = $1,161.45       $1,278.3753   $1,278.38   $1,278.35   $1,278.40