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 $32.59   12.241%   $36.5793   $36.58   $36.60   $36.60  
  Purchase #2 $223.98   7.614%   $241.0338   $241.03   $241.05   $241.00  
  Purchase #3 $196.74   10.374%   $217.1498   $217.15   $217.15   $217.10  
  Purchase #4 $112.95   5.111%   $118.7229   $118.72   $118.70   $118.70  
  Purchase #5 $157.72   4.574%   $164.9341   $164.93   $164.95   $164.90  
  Purchase #6 $16.60   5.534%   $17.5186   $17.52   $17.50   $17.50  
  Purchase #7 $203.49   6.324%   $216.3587   $216.36   $216.35   $216.40  
  7 purchase totals = $944.07       $1,012.2972   $1,012.29   $1,012.30   $1,012.20