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 $70.90   8.846%   $77.1718   $77.17   $77.15   $77.20  
  Purchase #2 $228.51   11.858%   $255.6067   $255.61   $255.60   $255.60  
  Purchase #3 $96.88   7.177%   $103.8331   $103.83   $103.85   $103.80  
  Purchase #4 $149.98   7.720%   $161.5585   $161.56   $161.55   $161.60  
  Purchase #5 $233.75   8.329%   $253.219   $253.22   $253.20   $253.20  
  Purchase #6 $32.53   6.691%   $34.7066   $34.71   $34.70   $34.70  
  Purchase #7 $237.51   13.120%   $268.6713   $268.67   $268.65   $268.70  
  7 purchase totals = $1,050.06       $1,154.7670   $1,154.77   $1,154.70   $1,154.80