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 $74.29   11.600%   $82.9076   $82.91   $82.90   $82.90  
  Purchase #2 $144.52   3.470%   $149.5348   $149.53   $149.55   $149.50  
  Purchase #3 $86.53   7.316%   $92.8605   $92.86   $92.85   $92.90  
  Purchase #4 $241.39   6.550%   $257.201   $257.20   $257.20   $257.20  
  Purchase #5 $57.76   9.780%   $63.4089   $63.41   $63.40   $63.40  
  Purchase #6 $156.69   13.121%   $177.2493   $177.25   $177.25   $177.20  
  Purchase #7 $196.83   3.369%   $203.4612   $203.46   $203.45   $203.50  
  7 purchase totals = $958.01       $1,026.6233   $1,026.62   $1,026.60   $1,026.60