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 $24.37   5.858%   $25.7976   $25.80   $25.80   $25.80  
  Purchase #2 $118.83   11.704%   $132.7379   $132.74   $132.75   $132.70  
  Purchase #3 $247.91   4.386%   $258.7833   $258.78   $258.80   $258.80  
  Purchase #4 $57.51   4.216%   $59.9346   $59.93   $59.95   $59.90  
  Purchase #5 $61.29   5.684%   $64.7737   $64.77   $64.75   $64.80  
  Purchase #6 $241.87   12.207%   $271.3951   $271.40   $271.40   $271.40  
  Purchase #7 $216.33   13.256%   $245.0067   $245.01   $245.00   $245.00  
  7 purchase totals = $968.11       $1,058.4289   $1,058.43   $1,058.45   $1,058.40