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 $58.53   12.605%   $65.9077   $65.91   $65.90   $65.90  
  Purchase #2 $26.71   7.662%   $28.7565   $28.76   $28.75   $28.80  
  Purchase #3 $120.59   8.764%   $131.1585   $131.16   $131.15   $131.20  
  Purchase #4 $39.40   6.375%   $41.9118   $41.91   $41.90   $41.90  
  Purchase #5 $174.66   9.832%   $191.8326   $191.83   $191.85   $191.80  
  Purchase #6 $114.73   12.541%   $129.1183   $129.12   $129.10   $129.10  
  Purchase #7 $246.69   7.317%   $264.7403   $264.74   $264.75   $264.70  
  7 purchase totals = $781.31       $853.4257   $853.43   $853.40   $853.40