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 $226.34   8.456%   $245.4793   $245.48   $245.50   $245.50  
  Purchase #2 $99.40   5.552%   $104.9187   $104.92   $104.90   $104.90  
  Purchase #3 $161.40   8.422%   $174.9931   $174.99   $175.00   $175.00  
  Purchase #4 $81.94   3.160%   $84.5293   $84.53   $84.55   $84.50  
  Purchase #5 $61.73   9.474%   $67.5783   $67.58   $67.60   $67.60  
  Purchase #6 $240.87   11.129%   $267.6764   $267.68   $267.70   $267.70  
  Purchase #7 $189.29   6.216%   $201.0563   $201.06   $201.05   $201.10  
  7 purchase totals = $1,060.97       $1,146.2314   $1,146.24   $1,146.30   $1,146.30