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 $182.93   3.492%   $189.3179   $189.32   $189.30   $189.30  
  Purchase #2 $57.92   5.269%   $60.9718   $60.97   $60.95   $61.00  
  Purchase #3 $112.78   4.751%   $118.1382   $118.14   $118.15   $118.10  
  Purchase #4 $60.98   4.392%   $63.6582   $63.66   $63.65   $63.70  
  Purchase #5 $212.61   9.426%   $232.6506   $232.65   $232.65   $232.70  
  Purchase #6 $223.61   3.211%   $230.7901   $230.79   $230.80   $230.80  
  Purchase #7 $83.69   5.575%   $88.3557   $88.36   $88.35   $88.40  
  7 purchase totals = $934.52       $983.8825   $983.89   $983.85   $984.00