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 $61.96   4.869%   $64.9768   $64.98   $65.00   $65.00  
  Purchase #2 $178.91   8.818%   $194.6863   $194.69   $194.70   $194.70  
  Purchase #3 $182.70   11.342%   $203.4218   $203.42   $203.40   $203.40  
  Purchase #4 $197.94   11.160%   $220.0301   $220.03   $220.05   $220.00  
  Purchase #5 $233.95   11.510%   $260.8776   $260.88   $260.90   $260.90  
  Purchase #6 $232.48   4.580%   $243.1276   $243.13   $243.15   $243.10  
  Purchase #7 $239.65   5.334%   $252.4329   $252.43   $252.45   $252.40  
  7 purchase totals = $1,327.59       $1,439.5531   $1,439.56   $1,439.65   $1,439.50