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 $132.98   6.795%   $142.016   $142.02   $142.00   $142.00  
  Purchase #2 $210.44   11.755%   $235.1772   $235.18   $235.20   $235.20  
  Purchase #3 $152.49   11.674%   $170.2917   $170.29   $170.30   $170.30  
  Purchase #4 $85.61   6.678%   $91.327   $91.33   $91.35   $91.30  
  Purchase #5 $141.67   9.452%   $155.0606   $155.06   $155.05   $155.10  
  Purchase #6 $51.25   7.578%   $55.1337   $55.13   $55.15   $55.10  
  Purchase #7 $154.97   7.172%   $166.0844   $166.08   $166.10   $166.10  
  7 purchase totals = $929.41       $1,015.0906   $1,015.09   $1,015.15   $1,015.10