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 $183.26   10.785%   $203.0246   $203.02   $203.00   $203.00  
  Purchase #2 $61.81   7.294%   $66.3184   $66.32   $66.30   $66.30  
  Purchase #3 $182.88   5.442%   $192.8323   $192.83   $192.85   $192.80  
  Purchase #4 $233.42   5.634%   $246.5709   $246.57   $246.55   $246.60  
  Purchase #5 $67.50   5.409%   $71.1511   $71.15   $71.15   $71.20  
  Purchase #6 $232.52   11.814%   $259.9899   $259.99   $260.00   $260.00  
  Purchase #7 $250.34   8.317%   $271.1608   $271.16   $271.15   $271.20  
  7 purchase totals = $1,211.73       $1,311.0480   $1,311.04   $1,311.00   $1,311.10