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 $54.85   3.704%   $56.8816   $56.88   $56.90   $56.90  
  Purchase #2 $213.25   10.354%   $235.3299   $235.33   $235.35   $235.30  
  Purchase #3 $226.56   6.712%   $241.7667   $241.77   $241.75   $241.80  
  Purchase #4 $130.33   6.187%   $138.3935   $138.39   $138.40   $138.40  
  Purchase #5 $5.89   10.677%   $6.5189   $6.52   $6.50   $6.50  
  Purchase #6 $162.76   8.844%   $177.1545   $177.15   $177.15   $177.20  
  Purchase #7 $135.48   10.853%   $150.1836   $150.18   $150.20   $150.20  
  7 purchase totals = $929.12       $1,006.2287   $1,006.22   $1,006.25   $1,006.30