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 $91.89   6.622%   $97.975   $97.98   $98.00   $98.00  
  Purchase #2 $31.76   4.849%   $33.3   $33.30   $33.30   $33.30  
  Purchase #3 $244.49   11.515%   $272.643   $272.64   $272.65   $272.60  
  Purchase #4 $152.49   12.622%   $171.7373   $171.74   $171.75   $171.70  
  Purchase #5 $152.43   5.219%   $160.3853   $160.39   $160.40   $160.40  
  Purchase #6 $250.70   7.776%   $270.1944   $270.19   $270.20   $270.20  
  Purchase #7 $248.79   6.104%   $263.9761   $263.98   $264.00   $264.00  
  7 purchase totals = $1,172.55       $1,270.2111   $1,270.22   $1,270.30   $1,270.20