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 $233.74   5.582%   $246.7874   $246.79   $246.80   $246.80  
  Purchase #2 $198.51   12.179%   $222.6865   $222.69   $222.70   $222.70  
  Purchase #3 $88.41   6.350%   $94.024   $94.02   $94.00   $94.00  
  Purchase #4 $5.56   5.667%   $5.8751   $5.88   $5.90   $5.90  
  Purchase #5 $113.78   3.711%   $118.0024   $118.00   $118.00   $118.00  
  Purchase #6 $230.40   6.415%   $245.1802   $245.18   $245.20   $245.20  
  Purchase #7 $22.75   8.749%   $24.7404   $24.74   $24.75   $24.70  
  7 purchase totals = $893.15       $957.2960   $957.30   $957.35   $957.30