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 $16.70   9.437%   $18.276   $18.28   $18.30   $18.30  
  Purchase #2 $157.96   3.345%   $163.2438   $163.24   $163.25   $163.20  
  Purchase #3 $80.81   8.568%   $87.7338   $87.73   $87.75   $87.70  
  Purchase #4 $123.80   3.280%   $127.8606   $127.86   $127.85   $127.90  
  Purchase #5 $33.92   12.558%   $38.1797   $38.18   $38.20   $38.20  
  Purchase #6 $19.84   9.330%   $21.6911   $21.69   $21.70   $21.70  
  Purchase #7 $101.52   10.452%   $112.1309   $112.13   $112.15   $112.10  
  7 purchase totals = $534.55       $569.1159   $569.11   $569.20   $569.10