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 $221.67   5.648%   $234.1899   $234.19   $234.20   $234.20  
  Purchase #2 $247.80   12.177%   $277.9746   $277.97   $277.95   $278.00  
  Purchase #3 $173.75   9.856%   $190.8748   $190.87   $190.85   $190.90  
  Purchase #4 $180.37   12.835%   $203.5205   $203.52   $203.50   $203.50  
  Purchase #5 $186.97   13.282%   $211.8034   $211.80   $211.80   $211.80  
  Purchase #6 $214.41   5.796%   $226.8372   $226.84   $226.85   $226.80  
  Purchase #7 $6.88   3.487%   $7.1199   $7.12   $7.10   $7.10  
  7 purchase totals = $1,231.85       $1,352.3203   $1,352.31   $1,352.25   $1,352.30