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 $68.45   8.791%   $74.4674   $74.47   $74.45   $74.50  
  Purchase #2 $137.93   9.227%   $150.6568   $150.66   $150.65   $150.70  
  Purchase #3 $201.79   3.348%   $208.5459   $208.55   $208.55   $208.50  
  Purchase #4 $232.69   8.113%   $251.5681   $251.57   $251.55   $251.60  
  Purchase #5 $162.27   9.602%   $177.8512   $177.85   $177.85   $177.90  
  Purchase #6 $207.78   4.304%   $216.7229   $216.72   $216.70   $216.70  
  Purchase #7 $202.67   12.132%   $227.2579   $227.26   $227.25   $227.30  
  7 purchase totals = $1,213.58       $1,307.0702   $1,307.08   $1,307.00   $1,307.20