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 $202.74   11.458%   $225.9699   $225.97   $225.95   $226.00  
  Purchase #2 $29.89   11.745%   $33.4006   $33.40   $33.40   $33.40  
  Purchase #3 $230.77   7.339%   $247.7062   $247.71   $247.70   $247.70  
  Purchase #4 $120.35   10.160%   $132.5776   $132.58   $132.60   $132.60  
  Purchase #5 $239.63   9.413%   $262.1864   $262.19   $262.20   $262.20  
  Purchase #6 $150.32   6.584%   $160.2171   $160.22   $160.20   $160.20  
  Purchase #7 $208.57   7.321%   $223.8394   $223.84   $223.85   $223.80  
  7 purchase totals = $1,182.27       $1,285.8972   $1,285.91   $1,285.90   $1,285.90