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 $54.68   13.755%   $62.2012   $62.20   $62.20   $62.20  
  Purchase #2 $241.43   12.205%   $270.8965   $270.90   $270.90   $270.90  
  Purchase #3 $135.65   8.339%   $146.9619   $146.96   $146.95   $147.00  
  Purchase #4 $171.80   3.739%   $178.2236   $178.22   $178.20   $178.20  
  Purchase #5 $26.60   3.155%   $27.4392   $27.44   $27.45   $27.40  
  Purchase #6 $96.89   8.640%   $105.2613   $105.26   $105.25   $105.30  
  Purchase #7 $204.90   10.625%   $226.6706   $226.67   $226.65   $226.70  
  7 purchase totals = $931.95       $1,017.6543   $1,017.65   $1,017.60   $1,017.70