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 $44.60   11.541%   $49.7473   $49.75   $49.75   $49.70  
  Purchase #2 $184.52   8.194%   $199.6396   $199.64   $199.65   $199.60  
  Purchase #3 $95.66   12.592%   $107.7055   $107.71   $107.70   $107.70  
  Purchase #4 $94.41   5.518%   $99.6195   $99.62   $99.60   $99.60  
  Purchase #5 $204.56   7.503%   $219.9081   $219.91   $219.90   $219.90  
  Purchase #6 $224.26   9.155%   $244.791   $244.79   $244.80   $244.80  
  Purchase #7 $72.55   3.175%   $74.8535   $74.85   $74.85   $74.90  
  7 purchase totals = $920.56       $996.2645   $996.27   $996.25   $996.20