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 $46.49   12.279%   $52.1985   $52.20   $52.20   $52.20  
  Purchase #2 $132.97   9.581%   $145.7099   $145.71   $145.70   $145.70  
  Purchase #3 $146.96   4.809%   $154.0273   $154.03   $154.05   $154.00  
  Purchase #4 $204.85   13.630%   $232.7711   $232.77   $232.75   $232.80  
  Purchase #5 $15.84   3.673%   $16.4218   $16.42   $16.40   $16.40  
  Purchase #6 $157.60   8.841%   $171.5334   $171.53   $171.55   $171.50  
  Purchase #7 $109.57   11.675%   $122.3623   $122.36   $122.35   $122.40  
  7 purchase totals = $814.28       $895.0243   $895.02   $895.00   $895.00