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 $206.86   9.833%   $227.2005   $227.20   $227.20   $227.20  
  Purchase #2 $219.93   11.755%   $245.7828   $245.78   $245.80   $245.80  
  Purchase #3 $164.62   7.363%   $176.741   $176.74   $176.75   $176.70  
  Purchase #4 $230.64   9.471%   $252.4839   $252.48   $252.50   $252.50  
  Purchase #5 $106.48   13.490%   $120.8442   $120.84   $120.85   $120.80  
  Purchase #6 $166.28   4.200%   $173.2638   $173.26   $173.25   $173.30  
  Purchase #7 $55.42   5.830%   $58.651   $58.65   $58.65   $58.70  
  7 purchase totals = $1,150.23       $1,254.9672   $1,254.95   $1,255.00   $1,255.00