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 $167.48   10.203%   $184.568   $184.57   $184.55   $184.60  
  Purchase #2 $203.91   7.854%   $219.9251   $219.93   $219.95   $219.90  
  Purchase #3 $59.92   8.794%   $65.1894   $65.19   $65.20   $65.20  
  Purchase #4 $87.79   13.598%   $99.7277   $99.73   $99.75   $99.70  
  Purchase #5 $194.93   5.609%   $205.8636   $205.86   $205.85   $205.90  
  Purchase #6 $92.67   4.285%   $96.6409   $96.64   $96.65   $96.60  
  Purchase #7 $183.98   3.741%   $190.8627   $190.86   $190.85   $190.90  
  7 purchase totals = $990.68       $1,062.7774   $1,062.78   $1,062.80   $1,062.80