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 $46.39   4.601%   $48.5244   $48.52   $48.50   $48.50  
  Purchase #2 $190.28   11.435%   $212.0385   $212.04   $212.05   $212.00  
  Purchase #3 $54.68   13.756%   $62.2018   $62.20   $62.20   $62.20  
  Purchase #4 $192.65   11.137%   $214.1054   $214.11   $214.10   $214.10  
  Purchase #5 $250.51   4.755%   $262.4218   $262.42   $262.40   $262.40  
  Purchase #6 $221.72   9.263%   $242.2579   $242.26   $242.25   $242.30  
  Purchase #7 $147.96   9.260%   $161.6611   $161.66   $161.65   $161.70  
  7 purchase totals = $1,104.19       $1,203.2109   $1,203.21   $1,203.15   $1,203.20