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 $77.88   8.208%   $84.2724   $84.27   $84.25   $84.30  
  Purchase #2 $197.61   3.158%   $203.8505   $203.85   $203.85   $203.90  
  Purchase #3 $32.31   9.367%   $35.3365   $35.34   $35.35   $35.30  
  Purchase #4 $162.88   12.193%   $182.74   $182.74   $182.75   $182.70  
  Purchase #5 $216.92   12.834%   $244.7595   $244.76   $244.75   $244.80  
  Purchase #6 $196.78   7.250%   $211.0466   $211.05   $211.05   $211.00  
  Purchase #7 $110.92   10.847%   $122.9515   $122.95   $122.95   $123.00  
  7 purchase totals = $995.30       $1,084.9570   $1,084.96   $1,084.95   $1,085.00