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 $54.84   13.489%   $62.2374   $62.24   $62.25   $62.20  
  Purchase #2 $110.47   11.870%   $123.5828   $123.58   $123.60   $123.60  
  Purchase #3 $187.75   3.139%   $193.6435   $193.64   $193.65   $193.60  
  Purchase #4 $132.46   9.625%   $145.2093   $145.21   $145.20   $145.20  
  Purchase #5 $21.91   7.513%   $23.5561   $23.56   $23.55   $23.60  
  Purchase #6 $26.45   4.435%   $27.6231   $27.62   $27.60   $27.60  
  Purchase #7 $27.60   8.777%   $30.0225   $30.02   $30.00   $30.00  
  7 purchase totals = $561.48       $605.8747   $605.87   $605.85   $605.80