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 $111.42   6.484%   $118.6445   $118.64   $118.65   $118.60  
  Purchase #2 $142.57   6.387%   $151.6759   $151.68   $151.70   $151.70  
  Purchase #3 $82.75   12.106%   $92.7677   $92.77   $92.75   $92.80  
  Purchase #4 $129.54   4.481%   $135.3447   $135.34   $135.35   $135.30  
  Purchase #5 $142.83   13.312%   $161.8435   $161.84   $161.85   $161.80  
  Purchase #6 $162.66   5.476%   $171.5673   $171.57   $171.55   $171.60  
  Purchase #7 $211.26   6.199%   $224.356   $224.36   $224.35   $224.40  
  7 purchase totals = $983.03       $1,056.1996   $1,056.20   $1,056.20   $1,056.20