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 $48.75   6.261%   $51.8022   $51.80   $51.80   $51.80  
  Purchase #2 $217.47   13.567%   $246.9742   $246.97   $246.95   $247.00  
  Purchase #3 $229.36   5.547%   $242.0826   $242.08   $242.10   $242.10  
  Purchase #4 $146.60   3.631%   $151.923   $151.92   $151.90   $151.90  
  Purchase #5 $105.42   3.376%   $108.979   $108.98   $109.00   $109.00  
  Purchase #6 $240.27   6.536%   $255.974   $255.97   $255.95   $256.00  
  Purchase #7 $159.41   4.837%   $167.1207   $167.12   $167.10   $167.10  
  7 purchase totals = $1,147.28       $1,224.8557   $1,224.84   $1,224.80   $1,224.90