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 $86.31   10.470%   $95.3467   $95.35   $95.35   $95.30  
  Purchase #2 $12.76   12.650%   $14.3741   $14.37   $14.35   $14.40  
  Purchase #3 $137.30   12.173%   $154.0135   $154.01   $154.00   $154.00  
  Purchase #4 $24.45   3.707%   $25.3564   $25.36   $25.35   $25.40  
  Purchase #5 $128.77   4.215%   $134.1977   $134.20   $134.20   $134.20  
  Purchase #6 $15.71   10.743%   $17.3977   $17.40   $17.40   $17.40  
  Purchase #7 $173.39   6.655%   $184.9291   $184.93   $184.95   $184.90  
  7 purchase totals = $578.69       $625.6152   $625.62   $625.60   $625.60