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 $22.42   10.241%   $24.716   $24.72   $24.70   $24.70  
  Purchase #2 $204.46   6.463%   $217.6742   $217.67   $217.65   $217.70  
  Purchase #3 $225.27   4.732%   $235.9298   $235.93   $235.95   $235.90  
  Purchase #4 $229.26   12.484%   $257.8808   $257.88   $257.90   $257.90  
  Purchase #5 $124.78   6.700%   $133.1403   $133.14   $133.15   $133.10  
  Purchase #6 $222.45   10.733%   $246.3256   $246.33   $246.35   $246.30  
  Purchase #7 $238.86   5.391%   $251.7369   $251.74   $251.75   $251.70  
  7 purchase totals = $1,267.50       $1,367.4036   $1,367.41   $1,367.45   $1,367.30