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 $54.65   12.596%   $61.5337   $61.53   $61.55   $61.50  
  Purchase #2 $171.96   11.268%   $191.3365   $191.34   $191.35   $191.30  
  Purchase #3 $249.66   12.584%   $281.0772   $281.08   $281.10   $281.10  
  Purchase #4 $113.52   13.405%   $128.7374   $128.74   $128.75   $128.70  
  Purchase #5 $131.43   8.818%   $143.0195   $143.02   $143.00   $143.00  
  Purchase #6 $168.77   3.843%   $175.2558   $175.26   $175.25   $175.30  
  Purchase #7 $218.38   5.556%   $230.5132   $230.51   $230.50   $230.50  
  7 purchase totals = $1,108.37       $1,211.4733   $1,211.48   $1,211.50   $1,211.40