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 $64.92   6.137%   $68.9041   $68.90   $68.90   $68.90  
  Purchase #2 $118.90   4.172%   $123.8605   $123.86   $123.85   $123.90  
  Purchase #3 $208.53   7.742%   $224.6744   $224.67   $224.65   $224.70  
  Purchase #4 $93.69   3.643%   $97.1031   $97.10   $97.10   $97.10  
  Purchase #5 $196.55   7.696%   $211.6765   $211.68   $211.70   $211.70  
  Purchase #6 $234.36   8.640%   $254.6087   $254.61   $254.60   $254.60  
  Purchase #7 $194.25   11.603%   $216.7888   $216.79   $216.80   $216.80  
  7 purchase totals = $1,111.20       $1,197.6161   $1,197.61   $1,197.60   $1,197.70