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 $34.93   10.456%   $38.5823   $38.58   $38.60   $38.60  
  Purchase #2 $40.68   5.707%   $43.0016   $43.00   $43.00   $43.00  
  Purchase #3 $153.39   13.655%   $174.3354   $174.34   $174.35   $174.30  
  Purchase #4 $95.55   13.744%   $108.6824   $108.68   $108.70   $108.70  
  Purchase #5 $236.57   7.590%   $254.5257   $254.53   $254.55   $254.50  
  Purchase #6 $17.27   4.241%   $18.0024   $18.00   $18.00   $18.00  
  Purchase #7 $246.87   11.384%   $274.9737   $274.97   $274.95   $275.00  
  7 purchase totals = $825.26       $912.1035   $912.10   $912.15   $912.10