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 $63.45   8.711%   $68.9771   $68.98   $69.00   $69.00  
  Purchase #2 $34.33   3.260%   $35.4492   $35.45   $35.45   $35.40  
  Purchase #3 $167.32   5.816%   $177.0513   $177.05   $177.05   $177.10  
  Purchase #4 $87.26   5.131%   $91.7373   $91.74   $91.75   $91.70  
  Purchase #5 $59.62   6.591%   $63.5496   $63.55   $63.55   $63.50  
  Purchase #6 $208.81   5.377%   $220.0377   $220.04   $220.05   $220.00  
  Purchase #7 $217.37   5.516%   $229.3601   $229.36   $229.35   $229.40  
  7 purchase totals = $838.16       $886.1623   $886.17   $886.20   $886.10