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 $177.48   13.763%   $201.9066   $201.91   $201.90   $201.90  
  Purchase #2 $206.80   13.369%   $234.4471   $234.45   $234.45   $234.40  
  Purchase #3 $179.47   4.459%   $187.4726   $187.47   $187.45   $187.50  
  Purchase #4 $48.82   10.350%   $53.8729   $53.87   $53.85   $53.90  
  Purchase #5 $145.45   10.803%   $161.163   $161.16   $161.15   $161.20  
  Purchase #6 $200.35   8.811%   $218.0028   $218.00   $218.00   $218.00  
  Purchase #7 $6.96   5.792%   $7.3631   $7.36   $7.35   $7.40  
  7 purchase totals = $965.33       $1,064.2281   $1,064.22   $1,064.15   $1,064.30