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 $245.46   3.472%   $253.9824   $253.98   $254.00   $254.00  
  Purchase #2 $184.72   11.509%   $205.9794   $205.98   $206.00   $206.00  
  Purchase #3 $134.48   13.561%   $152.7168   $152.72   $152.70   $152.70  
  Purchase #4 $194.78   12.869%   $219.8462   $219.85   $219.85   $219.80  
  Purchase #5 $69.43   6.461%   $73.9159   $73.92   $73.90   $73.90  
  Purchase #6 $196.48   9.205%   $214.566   $214.57   $214.55   $214.60  
  Purchase #7 $139.51   4.535%   $145.8368   $145.84   $145.85   $145.80  
  7 purchase totals = $1,164.86       $1,266.8435   $1,266.86   $1,266.85   $1,266.80