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 $65.49   6.269%   $69.5956   $69.60   $69.60   $69.60  
  Purchase #2 $164.69   7.795%   $177.5276   $177.53   $177.55   $177.50  
  Purchase #3 $110.73   11.740%   $123.7297   $123.73   $123.75   $123.70  
  Purchase #4 $206.98   4.707%   $216.7225   $216.72   $216.70   $216.70  
  Purchase #5 $73.40   6.440%   $78.127   $78.13   $78.15   $78.10  
  Purchase #6 $230.66   5.497%   $243.3394   $243.34   $243.35   $243.30  
  Purchase #7 $119.85   5.381%   $126.2991   $126.30   $126.30   $126.30  
  7 purchase totals = $971.80       $1,035.3409   $1,035.35   $1,035.40   $1,035.20