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 $153.42   8.598%   $166.6111   $166.61   $166.60   $166.60  
  Purchase #2 $204.59   11.305%   $227.7189   $227.72   $227.70   $227.70  
  Purchase #3 $30.58   11.701%   $34.1582   $34.16   $34.15   $34.20  
  Purchase #4 $84.88   11.839%   $94.9289   $94.93   $94.95   $94.90  
  Purchase #5 $118.93   13.835%   $135.384   $135.38   $135.40   $135.40  
  Purchase #6 $137.41   3.604%   $142.3623   $142.36   $142.35   $142.40  
  Purchase #7 $110.80   9.326%   $121.1332   $121.13   $121.15   $121.10  
  7 purchase totals = $840.61       $922.2966   $922.29   $922.30   $922.30