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 $211.62   8.480%   $229.5654   $229.57   $229.55   $229.60  
  Purchase #2 $111.77   6.775%   $119.3424   $119.34   $119.35   $119.30  
  Purchase #3 $154.79   7.246%   $166.0061   $166.01   $166.00   $166.00  
  Purchase #4 $176.61   8.672%   $191.9256   $191.93   $191.95   $191.90  
  Purchase #5 $31.98   8.595%   $34.7287   $34.73   $34.75   $34.70  
  Purchase #6 $204.70   7.129%   $219.2931   $219.29   $219.30   $219.30  
  Purchase #7 $102.39   4.852%   $107.358   $107.36   $107.35   $107.40  
  7 purchase totals = $993.86       $1,068.2193   $1,068.23   $1,068.25   $1,068.20