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 $144.80   7.704%   $155.9554   $155.96   $155.95   $156.00  
  Purchase #2 $170.35   4.685%   $178.3309   $178.33   $178.35   $178.30  
  Purchase #3 $189.65   8.610%   $205.9789   $205.98   $206.00   $206.00  
  Purchase #4 $66.39   7.435%   $71.3261   $71.33   $71.35   $71.30  
  Purchase #5 $246.66   9.437%   $269.9373   $269.94   $269.95   $269.90  
  Purchase #6 $233.69   10.174%   $257.4656   $257.47   $257.45   $257.50  
  Purchase #7 $130.56   3.376%   $134.9677   $134.97   $134.95   $135.00  
  7 purchase totals = $1,182.10       $1,273.9619   $1,273.98   $1,274.00   $1,274.00