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 $184.48   13.655%   $209.6707   $209.67   $209.65   $209.70  
  Purchase #2 $138.81   5.662%   $146.6694   $146.67   $146.65   $146.70  
  Purchase #3 $138.46   13.547%   $157.2172   $157.22   $157.20   $157.20  
  Purchase #4 $87.66   8.410%   $95.0322   $95.03   $95.05   $95.00  
  Purchase #5 $83.57   11.535%   $93.2098   $93.21   $93.20   $93.20  
  Purchase #6 $127.34   12.161%   $142.8258   $142.83   $142.85   $142.80  
  Purchase #7 $216.46   8.547%   $234.9608   $234.96   $234.95   $235.00  
  7 purchase totals = $976.78       $1,079.5859   $1,079.59   $1,079.55   $1,079.60