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 $85.48   11.793%   $95.5607   $95.56   $95.55   $95.60  
  Purchase #2 $66.47   5.584%   $70.1817   $70.18   $70.20   $70.20  
  Purchase #3 $210.33   6.191%   $223.3515   $223.35   $223.35   $223.40  
  Purchase #4 $63.48   11.347%   $70.6831   $70.68   $70.70   $70.70  
  Purchase #5 $227.52   3.645%   $235.8131   $235.81   $235.80   $235.80  
  Purchase #6 $93.51   10.737%   $103.5502   $103.55   $103.55   $103.60  
  Purchase #7 $85.66   3.753%   $88.8748   $88.87   $88.85   $88.90  
  7 purchase totals = $832.45       $888.0151   $888.00   $888.00   $888.20