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 $141.76   13.354%   $160.6906   $160.69   $160.70   $160.70  
  Purchase #2 $212.60   9.393%   $232.5695   $232.57   $232.55   $232.60  
  Purchase #3 $88.41   13.329%   $100.1942   $100.19   $100.20   $100.20  
  Purchase #4 $209.46   12.297%   $235.2173   $235.22   $235.20   $235.20  
  Purchase #5 $85.33   10.557%   $94.3383   $94.34   $94.35   $94.30  
  Purchase #6 $161.61   9.333%   $176.6931   $176.69   $176.70   $176.70  
  Purchase #7 $165.85   11.175%   $184.3837   $184.38   $184.40   $184.40  
  7 purchase totals = $1,065.02       $1,184.0867   $1,184.08   $1,184.10   $1,184.10