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 $53.28   12.559%   $59.9714   $59.97   $59.95   $60.00  
  Purchase #2 $20.85   10.869%   $23.1162   $23.12   $23.10   $23.10  
  Purchase #3 $243.95   12.371%   $274.1291   $274.13   $274.15   $274.10  
  Purchase #4 $225.75   3.506%   $233.6648   $233.66   $233.65   $233.70  
  Purchase #5 $84.71   9.245%   $92.5414   $92.54   $92.55   $92.50  
  Purchase #6 $249.86   7.712%   $269.1292   $269.13   $269.15   $269.10  
  Purchase #7 $84.56   12.861%   $95.4353   $95.44   $95.45   $95.40  
  7 purchase totals = $962.96       $1,047.9874   $1,047.99   $1,048.00   $1,047.90