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 $223.64   13.841%   $254.594   $254.59   $254.60   $254.60  
  Purchase #2 $86.69   8.206%   $93.8038   $93.80   $93.80   $93.80  
  Purchase #3 $20.83   5.639%   $22.0046   $22.00   $22.00   $22.00  
  Purchase #4 $247.35   5.431%   $260.7836   $260.78   $260.80   $260.80  
  Purchase #5 $21.36   10.219%   $23.5428   $23.54   $23.55   $23.50  
  Purchase #6 $247.50   13.106%   $279.9374   $279.94   $279.95   $279.90  
  Purchase #7 $205.29   13.464%   $232.9302   $232.93   $232.95   $232.90  
  7 purchase totals = $1,052.66       $1,167.5964   $1,167.58   $1,167.65   $1,167.50