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 $134.91   12.612%   $151.9248   $151.92   $151.90   $151.90  
  Purchase #2 $245.41   3.192%   $253.2435   $253.24   $253.25   $253.20  
  Purchase #3 $88.63   3.348%   $91.5973   $91.60   $91.60   $91.60  
  Purchase #4 $156.44   3.681%   $162.1986   $162.20   $162.20   $162.20  
  Purchase #5 $53.29   6.384%   $56.692   $56.69   $56.70   $56.70  
  Purchase #6 $203.95   7.142%   $218.5161   $218.52   $218.50   $218.50  
  Purchase #7 $87.88   5.349%   $92.5807   $92.58   $92.60   $92.60  
  7 purchase totals = $970.51       $1,026.7530   $1,026.75   $1,026.75   $1,026.70