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 $196.34   5.541%   $207.2192   $207.22   $207.20   $207.20  
  Purchase #2 $5.47   10.383%   $6.038   $6.04   $6.05   $6.00  
  Purchase #3 $50.41   9.499%   $55.1984   $55.20   $55.20   $55.20  
  Purchase #4 $110.96   7.286%   $119.0445   $119.04   $119.05   $119.00  
  Purchase #5 $124.48   6.193%   $132.189   $132.19   $132.20   $132.20  
  Purchase #6 $153.39   7.756%   $165.2869   $165.29   $165.30   $165.30  
  Purchase #7 $237.59   3.578%   $246.091   $246.09   $246.10   $246.10  
  7 purchase totals = $878.64       $931.0670   $931.07   $931.10   $931.00