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 $32.27   10.323%   $35.6012   $35.60   $35.60   $35.60  
  Purchase #2 $167.55   11.469%   $186.7663   $186.77   $186.75   $186.80  
  Purchase #3 $116.38   10.732%   $128.8699   $128.87   $128.85   $128.90  
  Purchase #4 $181.52   5.492%   $191.4891   $191.49   $191.50   $191.50  
  Purchase #5 $135.67   8.189%   $146.78   $146.78   $146.80   $146.80  
  Purchase #6 $43.81   12.158%   $49.1364   $49.14   $49.15   $49.10  
  Purchase #7 $99.79   13.803%   $113.564   $113.56   $113.55   $113.60  
  7 purchase totals = $776.99       $852.2069   $852.21   $852.20   $852.30