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 $142.66   8.607%   $154.9387   $154.94   $154.95   $154.90  
  Purchase #2 $163.83   11.326%   $182.3854   $182.39   $182.40   $182.40  
  Purchase #3 $178.34   13.508%   $202.4302   $202.43   $202.45   $202.40  
  Purchase #4 $63.92   9.410%   $69.9349   $69.93   $69.95   $69.90  
  Purchase #5 $166.80   7.522%   $179.3467   $179.35   $179.35   $179.30  
  Purchase #6 $88.71   3.829%   $92.1067   $92.11   $92.10   $92.10  
  Purchase #7 $160.93   5.525%   $169.8214   $169.82   $169.80   $169.80  
  7 purchase totals = $965.19       $1,050.9640   $1,050.97   $1,051.00   $1,050.80