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 $196.35   10.807%   $217.5695   $217.57   $217.55   $217.60  
  Purchase #2 $41.63   12.772%   $46.947   $46.95   $46.95   $46.90  
  Purchase #3 $248.99   8.534%   $270.2388   $270.24   $270.25   $270.20  
  Purchase #4 $67.42   5.526%   $71.1456   $71.15   $71.15   $71.10  
  Purchase #5 $204.79   6.270%   $217.6303   $217.63   $217.65   $217.60  
  Purchase #6 $156.52   8.339%   $169.5722   $169.57   $169.55   $169.60  
  Purchase #7 $75.90   5.544%   $80.1079   $80.11   $80.10   $80.10  
  7 purchase totals = $991.60       $1,073.2113   $1,073.22   $1,073.20   $1,073.10