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 $87.88   11.638%   $98.1075   $98.11   $98.10   $98.10  
  Purchase #2 $130.89   3.314%   $135.2277   $135.23   $135.25   $135.20  
  Purchase #3 $152.93   10.437%   $168.8913   $168.89   $168.90   $168.90  
  Purchase #4 $55.69   3.390%   $57.5779   $57.58   $57.60   $57.60  
  Purchase #5 $190.45   7.766%   $205.2403   $205.24   $205.25   $205.20  
  Purchase #6 $203.96   3.708%   $211.5228   $211.52   $211.50   $211.50  
  Purchase #7 $8.67   8.585%   $9.4143   $9.41   $9.40   $9.40  
  7 purchase totals = $830.47       $885.9818   $885.98   $886.00   $885.90