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 $48.92   6.754%   $52.2241   $52.22   $52.20   $52.20  
  Purchase #2 $187.46   9.375%   $205.0344   $205.03   $205.05   $205.00  
  Purchase #3 $61.69   4.295%   $64.3396   $64.34   $64.35   $64.30  
  Purchase #4 $205.78   5.483%   $217.0629   $217.06   $217.05   $217.10  
  Purchase #5 $187.91   9.421%   $205.613   $205.61   $205.60   $205.60  
  Purchase #6 $141.80   6.175%   $150.5562   $150.56   $150.55   $150.60  
  Purchase #7 $206.55   11.783%   $230.8878   $230.89   $230.90   $230.90  
  7 purchase totals = $1,040.11       $1,125.7180   $1,125.71   $1,125.70   $1,125.70