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 $83.56   13.426%   $94.7788   $94.78   $94.80   $94.80  
  Purchase #2 $80.32   8.261%   $86.9552   $86.96   $86.95   $87.00  
  Purchase #3 $85.48   10.766%   $94.6828   $94.68   $94.70   $94.70  
  Purchase #4 $239.89   13.396%   $272.0257   $272.03   $272.05   $272.00  
  Purchase #5 $213.70   6.803%   $228.238   $228.24   $228.25   $228.20  
  Purchase #6 $183.48   9.842%   $201.5381   $201.54   $201.55   $201.50  
  Purchase #7 $248.98   4.533%   $260.2663   $260.27   $260.25   $260.30  
  7 purchase totals = $1,135.41       $1,238.4849   $1,238.50   $1,238.55   $1,238.50