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 $23.46   10.498%   $25.9228   $25.92   $25.90   $25.90  
  Purchase #2 $223.59   10.830%   $247.8048   $247.80   $247.80   $247.80  
  Purchase #3 $194.59   3.715%   $201.819   $201.82   $201.80   $201.80  
  Purchase #4 $138.77   4.841%   $145.4879   $145.49   $145.50   $145.50  
  Purchase #5 $112.98   8.852%   $122.981   $122.98   $123.00   $123.00  
  Purchase #6 $55.47   3.648%   $57.4935   $57.49   $57.50   $57.50  
  Purchase #7 $232.73   7.506%   $250.1987   $250.20   $250.20   $250.20  
  7 purchase totals = $981.59       $1,051.7077   $1,051.70   $1,051.70   $1,051.70