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 $21.32   8.191%   $23.0663   $23.07   $23.05   $23.10  
  Purchase #2 $21.56   8.821%   $23.4618   $23.46   $23.45   $23.50  
  Purchase #3 $228.57   9.297%   $249.8202   $249.82   $249.80   $249.80  
  Purchase #4 $208.75   12.146%   $234.1048   $234.10   $234.10   $234.10  
  Purchase #5 $231.85   11.235%   $257.8983   $257.90   $257.90   $257.90  
  Purchase #6 $79.52   9.656%   $87.1985   $87.20   $87.20   $87.20  
  Purchase #7 $211.88   13.523%   $240.5325   $240.53   $240.55   $240.50  
  7 purchase totals = $1,003.45       $1,116.0824   $1,116.08   $1,116.05   $1,116.10