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 $141.90   4.665%   $148.5196   $148.52   $148.50   $148.50  
  Purchase #2 $180.26   3.318%   $186.241   $186.24   $186.25   $186.20  
  Purchase #3 $191.88   6.856%   $205.0353   $205.04   $205.05   $205.00  
  Purchase #4 $12.35   10.288%   $13.6206   $13.62   $13.60   $13.60  
  Purchase #5 $37.86   4.844%   $39.6939   $39.69   $39.70   $39.70  
  Purchase #6 $88.48   12.741%   $99.7532   $99.75   $99.75   $99.80  
  Purchase #7 $23.43   10.203%   $25.8206   $25.82   $25.80   $25.80  
  7 purchase totals = $676.16       $718.6842   $718.68   $718.65   $718.60