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 $118.66   13.564%   $134.755   $134.76   $134.75   $134.80  
  Purchase #2 $220.32   5.722%   $232.9267   $232.93   $232.95   $232.90  
  Purchase #3 $8.98   5.694%   $9.4913   $9.49   $9.50   $9.50  
  Purchase #4 $134.29   4.701%   $140.603   $140.60   $140.60   $140.60  
  Purchase #5 $128.46   4.280%   $133.9581   $133.96   $133.95   $134.00  
  Purchase #6 $221.81   10.861%   $245.9008   $245.90   $245.90   $245.90  
  Purchase #7 $179.49   12.845%   $202.5455   $202.55   $202.55   $202.50  
  7 purchase totals = $1,012.01       $1,100.1804   $1,100.19   $1,100.20   $1,100.20