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 $62.51   9.682%   $68.5622   $68.56   $68.55   $68.60  
  Purchase #2 $10.43   10.387%   $11.5134   $11.51   $11.50   $11.50  
  Purchase #3 $109.99   13.387%   $124.7144   $124.71   $124.70   $124.70  
  Purchase #4 $20.37   10.184%   $22.4445   $22.44   $22.45   $22.40  
  Purchase #5 $239.97   7.803%   $258.6949   $258.69   $258.70   $258.70  
  Purchase #6 $113.36   6.415%   $120.632   $120.63   $120.65   $120.60  
  Purchase #7 $220.69   10.311%   $243.4453   $243.45   $243.45   $243.40  
  7 purchase totals = $777.32       $850.0067   $849.99   $850.00   $849.90