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 $55.31   11.805%   $61.8393   $61.84   $61.85   $61.80  
  Purchase #2 $110.53   12.779%   $124.6546   $124.65   $124.65   $124.70  
  Purchase #3 $160.87   3.334%   $166.2334   $166.23   $166.25   $166.20  
  Purchase #4 $192.26   5.874%   $203.5534   $203.55   $203.55   $203.60  
  Purchase #5 $113.27   11.515%   $126.313   $126.31   $126.30   $126.30  
  Purchase #6 $197.74   10.646%   $218.7914   $218.79   $218.80   $218.80  
  Purchase #7 $167.78   10.478%   $185.36   $185.36   $185.35   $185.40  
  7 purchase totals = $997.76       $1,086.7451   $1,086.73   $1,086.75   $1,086.80