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 $195.25   8.256%   $211.3698   $211.37   $211.35   $211.40  
  Purchase #2 $65.44   8.395%   $70.9337   $70.93   $70.95   $70.90  
  Purchase #3 $9.91   6.107%   $10.5152   $10.52   $10.50   $10.50  
  Purchase #4 $33.66   12.220%   $37.7733   $37.77   $37.75   $37.80  
  Purchase #5 $138.26   9.579%   $151.5039   $151.50   $151.50   $151.50  
  Purchase #6 $155.44   8.701%   $168.9648   $168.96   $168.95   $169.00  
  Purchase #7 $250.73   5.736%   $265.1119   $265.11   $265.10   $265.10  
  7 purchase totals = $848.69       $916.1726   $916.16   $916.10   $916.20