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 $198.65   10.273%   $219.0573   $219.06   $219.05   $219.10  
  Purchase #2 $164.51   11.657%   $183.6869   $183.69   $183.70   $183.70  
  Purchase #3 $158.28   13.541%   $179.7127   $179.71   $179.70   $179.70  
  Purchase #4 $73.95   4.296%   $77.1269   $77.13   $77.15   $77.10  
  Purchase #5 $16.79   9.753%   $18.4275   $18.43   $18.45   $18.40  
  Purchase #6 $79.97   4.251%   $83.3695   $83.37   $83.35   $83.40  
  Purchase #7 $186.43   8.325%   $201.9503   $201.95   $201.95   $202.00  
  7 purchase totals = $878.58       $963.3311   $963.34   $963.35   $963.40