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 $216.53   11.802%   $242.0849   $242.08   $242.10   $242.10  
  Purchase #2 $212.75   13.416%   $241.2925   $241.29   $241.30   $241.30  
  Purchase #3 $52.51   4.413%   $54.8273   $54.83   $54.85   $54.80  
  Purchase #4 $173.85   8.860%   $189.2531   $189.25   $189.25   $189.30  
  Purchase #5 $247.57   13.853%   $281.8659   $281.87   $281.85   $281.90  
  Purchase #6 $108.80   3.203%   $112.2849   $112.28   $112.30   $112.30  
  Purchase #7 $223.93   8.756%   $243.5373   $243.54   $243.55   $243.50  
  7 purchase totals = $1,235.94       $1,365.1459   $1,365.14   $1,365.20   $1,365.20