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 $55.97   10.292%   $61.7304   $61.73   $61.75   $61.70  
  Purchase #2 $192.30   12.766%   $216.849   $216.85   $216.85   $216.80  
  Purchase #3 $159.56   11.355%   $177.678   $177.68   $177.70   $177.70  
  Purchase #4 $97.75   10.768%   $108.2757   $108.28   $108.30   $108.30  
  Purchase #5 $196.59   3.604%   $203.6751   $203.68   $203.70   $203.70  
  Purchase #6 $127.98   7.634%   $137.75   $137.75   $137.75   $137.80  
  Purchase #7 $65.33   6.839%   $69.7979   $69.80   $69.80   $69.80  
  7 purchase totals = $895.48       $975.7561   $975.77   $975.85   $975.80