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 $48.65   3.728%   $50.4637   $50.46   $50.45   $50.50  
  Purchase #2 $182.68   6.419%   $194.4062   $194.41   $194.40   $194.40  
  Purchase #3 $161.82   11.493%   $180.418   $180.42   $180.40   $180.40  
  Purchase #4 $87.68   9.286%   $95.822   $95.82   $95.80   $95.80  
  Purchase #5 $229.25   5.644%   $242.1889   $242.19   $242.20   $242.20  
  Purchase #6 $171.49   7.311%   $184.0276   $184.03   $184.05   $184.00  
  Purchase #7 $245.43   12.370%   $275.7897   $275.79   $275.80   $275.80  
  7 purchase totals = $1,127.00       $1,223.1161   $1,223.12   $1,223.10   $1,223.10