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 $173.57   8.606%   $188.5074   $188.51   $188.50   $188.50  
  Purchase #2 $54.53   13.734%   $62.0192   $62.02   $62.00   $62.00  
  Purchase #3 $157.30   6.605%   $167.6897   $167.69   $167.70   $167.70  
  Purchase #4 $204.64   6.681%   $218.312   $218.31   $218.30   $218.30  
  Purchase #5 $198.96   10.504%   $219.8588   $219.86   $219.85   $219.90  
  Purchase #6 $22.97   9.107%   $25.0619   $25.06   $25.05   $25.10  
  Purchase #7 $133.60   6.256%   $141.958   $141.96   $141.95   $142.00  
  7 purchase totals = $945.57       $1,023.4070   $1,023.41   $1,023.35   $1,023.50