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 $89.63   7.636%   $96.4741   $96.47   $96.45   $96.50  
  Purchase #2 $135.73   13.450%   $153.9857   $153.99   $154.00   $154.00  
  Purchase #3 $230.75   9.575%   $252.8443   $252.84   $252.85   $252.80  
  Purchase #4 $23.87   11.423%   $26.5967   $26.60   $26.60   $26.60  
  Purchase #5 $100.92   12.473%   $113.5078   $113.51   $113.50   $113.50  
  Purchase #6 $160.93   11.492%   $179.4241   $179.42   $179.40   $179.40  
  Purchase #7 $209.55   12.322%   $235.3708   $235.37   $235.35   $235.40  
  7 purchase totals = $951.38       $1,058.2035   $1,058.20   $1,058.15   $1,058.20