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 $188.74   8.496%   $204.7754   $204.78   $204.80   $204.80  
  Purchase #2 $44.51   13.583%   $50.5558   $50.56   $50.55   $50.60  
  Purchase #3 $79.64   5.673%   $84.158   $84.16   $84.15   $84.20  
  Purchase #4 $244.89   12.586%   $275.7119   $275.71   $275.70   $275.70  
  Purchase #5 $239.34   6.335%   $254.5022   $254.50   $254.50   $254.50  
  Purchase #6 $50.48   4.204%   $52.6022   $52.60   $52.60   $52.60  
  Purchase #7 $127.50   4.600%   $133.365   $133.37   $133.35   $133.40  
  7 purchase totals = $975.10       $1,055.6705   $1,055.68   $1,055.65   $1,055.80