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 $87.92   4.541%   $91.9124   $91.91   $91.90   $91.90  
  Purchase #2 $133.97   9.658%   $146.9088   $146.91   $146.90   $146.90  
  Purchase #3 $9.67   6.784%   $10.326   $10.33   $10.35   $10.30  
  Purchase #4 $212.34   6.841%   $226.8662   $226.87   $226.85   $226.90  
  Purchase #5 $13.93   5.592%   $14.709   $14.71   $14.70   $14.70  
  Purchase #6 $193.47   6.806%   $206.6376   $206.64   $206.65   $206.60  
  Purchase #7 $243.43   5.848%   $257.6658   $257.67   $257.65   $257.70  
  7 purchase totals = $894.73       $955.0258   $955.04   $955.00   $955.00