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 $64.76   6.474%   $68.9526   $68.95   $68.95   $69.00  
  Purchase #2 $15.42   7.532%   $16.5814   $16.58   $16.60   $16.60  
  Purchase #3 $232.88   4.581%   $243.5482   $243.55   $243.55   $243.50  
  Purchase #4 $215.98   5.297%   $227.4205   $227.42   $227.40   $227.40  
  Purchase #5 $226.84   7.348%   $243.5082   $243.51   $243.50   $243.50  
  Purchase #6 $60.68   4.599%   $63.4707   $63.47   $63.45   $63.50  
  Purchase #7 $205.29   7.831%   $221.3663   $221.37   $221.35   $221.40  
  7 purchase totals = $1,021.85       $1,084.8479   $1,084.85   $1,084.80   $1,084.90