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 $201.45   12.519%   $226.6695   $226.67   $226.65   $226.70  
  Purchase #2 $96.53   8.558%   $104.791   $104.79   $104.80   $104.80  
  Purchase #3 $60.98   8.844%   $66.3731   $66.37   $66.35   $66.40  
  Purchase #4 $167.45   12.176%   $187.8387   $187.84   $187.85   $187.80  
  Purchase #5 $26.40   10.693%   $29.223   $29.22   $29.20   $29.20  
  Purchase #6 $95.35   4.413%   $99.5578   $99.56   $99.55   $99.60  
  Purchase #7 $28.52   10.176%   $31.4222   $31.42   $31.40   $31.40  
  7 purchase totals = $676.68       $745.8753   $745.87   $745.80   $745.90