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 $145.94   11.697%   $163.0106   $163.01   $163.00   $163.00  
  Purchase #2 $211.88   8.682%   $230.2754   $230.28   $230.30   $230.30  
  Purchase #3 $68.31   6.811%   $72.9626   $72.96   $72.95   $73.00  
  Purchase #4 $43.92   10.612%   $48.5808   $48.58   $48.60   $48.60  
  Purchase #5 $100.43   3.378%   $103.8225   $103.82   $103.80   $103.80  
  Purchase #6 $67.52   8.638%   $73.3524   $73.35   $73.35   $73.40  
  Purchase #7 $248.88   8.339%   $269.6341   $269.63   $269.65   $269.60  
  7 purchase totals = $886.88       $961.6384   $961.63   $961.65   $961.70