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 $31.86   12.484%   $35.8374   $35.84   $35.85   $35.80  
  Purchase #2 $26.52   10.596%   $29.3301   $29.33   $29.35   $29.30  
  Purchase #3 $54.42   9.767%   $59.7352   $59.74   $59.75   $59.70  
  Purchase #4 $242.96   8.123%   $262.6956   $262.70   $262.70   $262.70  
  Purchase #5 $183.72   6.683%   $195.998   $196.00   $196.00   $196.00  
  Purchase #6 $214.84   7.340%   $230.6093   $230.61   $230.60   $230.60  
  Purchase #7 $202.46   8.400%   $219.4666   $219.47   $219.45   $219.50  
  7 purchase totals = $956.78       $1,033.6722   $1,033.69   $1,033.70   $1,033.60