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 $41.54   6.803%   $44.366   $44.37   $44.35   $44.40  
  Purchase #2 $205.74   6.499%   $219.111   $219.11   $219.10   $219.10  
  Purchase #3 $126.38   4.392%   $131.9306   $131.93   $131.95   $131.90  
  Purchase #4 $137.93   5.576%   $145.621   $145.62   $145.60   $145.60  
  Purchase #5 $62.37   9.677%   $68.4055   $68.41   $68.40   $68.40  
  Purchase #6 $244.64   8.562%   $265.5861   $265.59   $265.60   $265.60  
  Purchase #7 $237.69   3.255%   $245.4268   $245.43   $245.45   $245.40  
  7 purchase totals = $1,056.29       $1,120.4470   $1,120.46   $1,120.45   $1,120.40