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 $147.76   12.348%   $166.0054   $166.01   $166.00   $166.00  
  Purchase #2 $43.62   5.463%   $46.003   $46.00   $46.00   $46.00  
  Purchase #3 $227.55   7.213%   $243.9632   $243.96   $243.95   $244.00  
  Purchase #4 $75.90   13.477%   $86.129   $86.13   $86.15   $86.10  
  Purchase #5 $64.75   6.739%   $69.1135   $69.11   $69.10   $69.10  
  Purchase #6 $44.48   8.279%   $48.1625   $48.16   $48.15   $48.20  
  Purchase #7 $188.89   7.444%   $202.951   $202.95   $202.95   $203.00  
  7 purchase totals = $792.95       $862.3276   $862.32   $862.30   $862.40