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 $86.92   6.203%   $92.3116   $92.31   $92.30   $92.30  
  Purchase #2 $149.56   6.717%   $159.6059   $159.61   $159.60   $159.60  
  Purchase #3 $226.62   4.686%   $237.2394   $237.24   $237.25   $237.20  
  Purchase #4 $232.28   3.812%   $241.1345   $241.13   $241.15   $241.10  
  Purchase #5 $232.68   3.359%   $240.4957   $240.50   $240.50   $240.50  
  Purchase #6 $131.35   3.292%   $135.674   $135.67   $135.65   $135.70  
  Purchase #7 $82.53   9.282%   $90.1904   $90.19   $90.20   $90.20  
  7 purchase totals = $1,141.94       $1,196.6515   $1,196.65   $1,196.65   $1,196.60