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 $168.34   3.219%   $173.7589   $173.76   $173.75   $173.80  
  Purchase #2 $58.74   3.126%   $60.5762   $60.58   $60.60   $60.60  
  Purchase #3 $236.56   8.618%   $256.9467   $256.95   $256.95   $256.90  
  Purchase #4 $11.35   8.593%   $12.3253   $12.33   $12.35   $12.30  
  Purchase #5 $47.52   3.427%   $49.1485   $49.15   $49.15   $49.10  
  Purchase #6 $156.40   11.741%   $174.7629   $174.76   $174.75   $174.80  
  Purchase #7 $61.26   13.363%   $69.4462   $69.45   $69.45   $69.40  
  7 purchase totals = $740.17       $796.9647   $796.98   $797.00   $796.90