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 $85.42   13.518%   $96.9671   $96.97   $96.95   $97.00  
  Purchase #2 $113.57   9.685%   $124.5693   $124.57   $124.55   $124.60  
  Purchase #3 $43.71   13.283%   $49.516   $49.52   $49.50   $49.50  
  Purchase #4 $180.60   13.580%   $205.1255   $205.13   $205.15   $205.10  
  Purchase #5 $45.37   10.624%   $50.1901   $50.19   $50.20   $50.20  
  Purchase #6 $5.36   11.145%   $5.9574   $5.96   $5.95   $6.00  
  Purchase #7 $241.52   8.865%   $262.9307   $262.93   $262.95   $262.90  
  7 purchase totals = $715.55       $795.2561   $795.27   $795.25   $795.30