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 $245.96   9.360%   $268.9819   $268.98   $269.00   $269.00  
  Purchase #2 $52.92   13.607%   $60.1208   $60.12   $60.10   $60.10  
  Purchase #3 $194.39   12.652%   $218.9842   $218.98   $219.00   $219.00  
  Purchase #4 $16.72   13.239%   $18.9336   $18.93   $18.95   $18.90  
  Purchase #5 $179.32   13.177%   $202.949   $202.95   $202.95   $202.90  
  Purchase #6 $26.36   13.367%   $29.8835   $29.88   $29.90   $29.90  
  Purchase #7 $215.56   7.385%   $231.4791   $231.48   $231.50   $231.50  
  7 purchase totals = $931.23       $1,031.3321   $1,031.32   $1,031.40   $1,031.30