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 $59.58   3.589%   $61.7183   $61.72   $61.70   $61.70  
  Purchase #2 $108.58   9.873%   $119.3001   $119.30   $119.30   $119.30  
  Purchase #3 $109.70   11.248%   $122.0391   $122.04   $122.05   $122.00  
  Purchase #4 $138.36   4.261%   $144.2555   $144.26   $144.25   $144.30  
  Purchase #5 $5.60   7.779%   $6.0356   $6.04   $6.05   $6.00  
  Purchase #6 $161.26   12.205%   $180.9418   $180.94   $180.95   $180.90  
  Purchase #7 $79.41   10.534%   $87.775   $87.78   $87.80   $87.80  
  7 purchase totals = $662.49       $722.0654   $722.08   $722.10   $722.00