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 $82.66   6.172%   $87.7618   $87.76   $87.75   $87.80  
  Purchase #2 $162.52   10.126%   $178.9768   $178.98   $179.00   $179.00  
  Purchase #3 $214.96   12.469%   $241.7634   $241.76   $241.75   $241.80  
  Purchase #4 $88.27   5.813%   $93.4011   $93.40   $93.40   $93.40  
  Purchase #5 $204.72   3.214%   $211.2997   $211.30   $211.30   $211.30  
  Purchase #6 $58.29   3.342%   $60.2381   $60.24   $60.25   $60.20  
  Purchase #7 $157.76   11.425%   $175.7841   $175.78   $175.80   $175.80  
  7 purchase totals = $969.18       $1,049.2250   $1,049.22   $1,049.25   $1,049.30