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 $219.96   8.252%   $238.1111   $238.11   $238.10   $238.10  
  Purchase #2 $62.78   10.102%   $69.122   $69.12   $69.10   $69.10  
  Purchase #3 $210.26   4.248%   $219.1918   $219.19   $219.20   $219.20  
  Purchase #4 $244.40   7.844%   $263.5707   $263.57   $263.55   $263.60  
  Purchase #5 $52.58   8.781%   $57.197   $57.20   $57.20   $57.20  
  Purchase #6 $65.47   7.717%   $70.5223   $70.52   $70.50   $70.50  
  Purchase #7 $11.86   12.234%   $13.311   $13.31   $13.30   $13.30  
  7 purchase totals = $867.31       $931.0259   $931.02   $930.95   $931.00