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 $93.80   4.453%   $97.9769   $97.98   $98.00   $98.00  
  Purchase #2 $5.41   8.752%   $5.8835   $5.88   $5.90   $5.90  
  Purchase #3 $203.79   7.197%   $218.4568   $218.46   $218.45   $218.50  
  Purchase #4 $130.57   11.457%   $145.5294   $145.53   $145.55   $145.50  
  Purchase #5 $245.65   5.412%   $258.9446   $258.94   $258.95   $258.90  
  Purchase #6 $42.80   4.771%   $44.842   $44.84   $44.85   $44.80  
  Purchase #7 $172.35   6.179%   $182.9995   $183.00   $183.00   $183.00  
  7 purchase totals = $894.37       $954.6327   $954.63   $954.70   $954.60