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 $207.59   8.155%   $224.519   $224.52   $224.50   $224.50  
  Purchase #2 $112.88   11.446%   $125.8002   $125.80   $125.80   $125.80  
  Purchase #3 $50.37   13.193%   $57.0153   $57.02   $57.00   $57.00  
  Purchase #4 $233.84   7.409%   $251.1652   $251.17   $251.15   $251.20  
  Purchase #5 $140.32   8.801%   $152.6696   $152.67   $152.65   $152.70  
  Purchase #6 $228.99   13.506%   $259.9174   $259.92   $259.90   $259.90  
  Purchase #7 $15.31   10.555%   $16.926   $16.93   $16.95   $16.90  
  7 purchase totals = $989.30       $1,088.0127   $1,088.03   $1,087.95   $1,088.00