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 $176.68   11.213%   $196.4911   $196.49   $196.50   $196.50  
  Purchase #2 $206.38   9.346%   $225.6683   $225.67   $225.65   $225.70  
  Purchase #3 $98.95   4.305%   $103.2098   $103.21   $103.20   $103.20  
  Purchase #4 $120.66   12.478%   $135.716   $135.72   $135.70   $135.70  
  Purchase #5 $26.76   5.497%   $28.231   $28.23   $28.25   $28.20  
  Purchase #6 $209.92   3.352%   $216.9565   $216.96   $216.95   $217.00  
  Purchase #7 $110.94   4.112%   $115.5019   $115.50   $115.50   $115.50  
  7 purchase totals = $950.29       $1,021.7746   $1,021.78   $1,021.75   $1,021.80