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 $119.66   6.292%   $127.189   $127.19   $127.20   $127.20  
  Purchase #2 $121.58   3.546%   $125.8912   $125.89   $125.90   $125.90  
  Purchase #3 $108.32   9.556%   $118.6711   $118.67   $118.65   $118.70  
  Purchase #4 $150.33   6.402%   $159.9541   $159.95   $159.95   $160.00  
  Purchase #5 $231.31   7.150%   $247.8487   $247.85   $247.85   $247.80  
  Purchase #6 $241.77   11.447%   $269.4454   $269.45   $269.45   $269.40  
  Purchase #7 $194.68   11.760%   $217.5744   $217.57   $217.55   $217.60  
  7 purchase totals = $1,167.65       $1,266.5739   $1,266.57   $1,266.55   $1,266.60