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 $60.96   5.411%   $64.2585   $64.26   $64.25   $64.30  
  Purchase #2 $174.52   12.111%   $195.6561   $195.66   $195.65   $195.70  
  Purchase #3 $184.97   4.840%   $193.9225   $193.92   $193.90   $193.90  
  Purchase #4 $151.42   12.374%   $170.1567   $170.16   $170.15   $170.20  
  Purchase #5 $207.73   13.413%   $235.5928   $235.59   $235.60   $235.60  
  Purchase #6 $27.71   5.334%   $29.1881   $29.19   $29.20   $29.20  
  Purchase #7 $215.87   11.807%   $241.3578   $241.36   $241.35   $241.40  
  7 purchase totals = $1,023.18       $1,130.1325   $1,130.14   $1,130.10   $1,130.30