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 $230.69   9.641%   $252.9308   $252.93   $252.95   $252.90  
  Purchase #2 $236.84   13.310%   $268.3634   $268.36   $268.35   $268.40  
  Purchase #3 $95.45   6.359%   $101.5197   $101.52   $101.50   $101.50  
  Purchase #4 $222.32   5.599%   $234.7677   $234.77   $234.75   $234.80  
  Purchase #5 $34.74   5.544%   $36.666   $36.67   $36.65   $36.70  
  Purchase #6 $90.81   12.399%   $102.0695   $102.07   $102.05   $102.10  
  Purchase #7 $220.41   10.616%   $243.8087   $243.81   $243.80   $243.80  
  7 purchase totals = $1,131.26       $1,240.1258   $1,240.13   $1,240.05   $1,240.20