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 $88.42   13.205%   $100.0959   $100.10   $100.10   $100.10  
  Purchase #2 $157.31   11.531%   $175.4494   $175.45   $175.45   $175.40  
  Purchase #3 $211.62   9.198%   $231.0848   $231.08   $231.10   $231.10  
  Purchase #4 $150.54   7.122%   $161.2615   $161.26   $161.25   $161.30  
  Purchase #5 $121.67   13.393%   $137.9653   $137.97   $137.95   $138.00  
  Purchase #6 $23.48   13.472%   $26.6432   $26.64   $26.65   $26.60  
  Purchase #7 $178.43   8.307%   $193.2522   $193.25   $193.25   $193.30  
  7 purchase totals = $931.47       $1,025.7523   $1,025.75   $1,025.75   $1,025.80