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 $93.98   5.260%   $98.9233   $98.92   $98.90   $98.90  
  Purchase #2 $247.75   11.549%   $276.3626   $276.36   $276.35   $276.40  
  Purchase #3 $24.79   8.802%   $26.972   $26.97   $26.95   $27.00  
  Purchase #4 $191.66   9.809%   $210.4599   $210.46   $210.45   $210.50  
  Purchase #5 $129.88   3.835%   $134.8609   $134.86   $134.85   $134.90  
  Purchase #6 $243.61   11.170%   $270.8212   $270.82   $270.80   $270.80  
  Purchase #7 $46.68   11.628%   $52.108   $52.11   $52.10   $52.10  
  7 purchase totals = $978.35       $1,070.5079   $1,070.50   $1,070.40   $1,070.60