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 $97.79   9.362%   $106.9451   $106.95   $106.95   $106.90  
  Purchase #2 $72.77   9.317%   $79.55   $79.55   $79.55   $79.60  
  Purchase #3 $26.79   11.187%   $29.787   $29.79   $29.80   $29.80  
  Purchase #4 $232.58   3.869%   $241.5785   $241.58   $241.60   $241.60  
  Purchase #5 $123.44   11.858%   $138.0775   $138.08   $138.10   $138.10  
  Purchase #6 $242.78   4.605%   $253.96   $253.96   $253.95   $254.00  
  Purchase #7 $101.98   3.261%   $105.3056   $105.31   $105.30   $105.30  
  7 purchase totals = $898.13       $955.2037   $955.22   $955.25   $955.30