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 $81.54   5.471%   $86.0011   $86.00   $86.00   $86.00  
  Purchase #2 $204.38   10.110%   $225.0428   $225.04   $225.05   $225.00  
  Purchase #3 $57.41   11.417%   $63.9645   $63.96   $63.95   $64.00  
  Purchase #4 $166.41   4.859%   $174.4959   $174.50   $174.50   $174.50  
  Purchase #5 $203.45   3.151%   $209.8607   $209.86   $209.85   $209.90  
  Purchase #6 $90.90   7.543%   $97.7566   $97.76   $97.75   $97.80  
  Purchase #7 $166.57   4.507%   $174.0773   $174.08   $174.10   $174.10  
  7 purchase totals = $970.66       $1,031.1989   $1,031.20   $1,031.20   $1,031.30