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 $241.39   5.856%   $255.5258   $255.53   $255.55   $255.50  
  Purchase #2 $206.84   5.865%   $218.9712   $218.97   $218.95   $219.00  
  Purchase #3 $132.66   5.394%   $139.8157   $139.82   $139.80   $139.80  
  Purchase #4 $127.35   6.764%   $135.964   $135.96   $135.95   $136.00  
  Purchase #5 $170.44   5.380%   $179.6097   $179.61   $179.60   $179.60  
  Purchase #6 $116.65   6.211%   $123.8951   $123.90   $123.90   $123.90  
  Purchase #7 $69.29   12.173%   $77.7247   $77.72   $77.70   $77.70  
  7 purchase totals = $1,064.62       $1,131.5062   $1,131.51   $1,131.45   $1,131.50