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 $61.47   12.306%   $69.0345   $69.03   $69.05   $69.00  
  Purchase #2 $220.45   13.650%   $250.5414   $250.54   $250.55   $250.50  
  Purchase #3 $231.90   12.445%   $260.76   $260.76   $260.75   $260.80  
  Purchase #4 $25.95   5.419%   $27.3562   $27.36   $27.35   $27.40  
  Purchase #5 $97.80   11.440%   $108.9883   $108.99   $109.00   $109.00  
  Purchase #6 $109.96   13.663%   $124.9838   $124.98   $125.00   $125.00  
  Purchase #7 $216.42   6.417%   $230.3077   $230.31   $230.30   $230.30  
  7 purchase totals = $963.95       $1,071.9719   $1,071.97   $1,072.00   $1,072.00