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 $178.55   13.160%   $202.0472   $202.05   $202.05   $202.00  
  Purchase #2 $178.43   13.215%   $202.0095   $202.01   $202.00   $202.00  
  Purchase #3 $175.41   6.255%   $186.3819   $186.38   $186.40   $186.40  
  Purchase #4 $32.83   8.743%   $35.7003   $35.70   $35.70   $35.70  
  Purchase #5 $233.92   13.327%   $265.0945   $265.09   $265.10   $265.10  
  Purchase #6 $194.61   3.679%   $201.7697   $201.77   $201.75   $201.80  
  Purchase #7 $68.37   12.683%   $77.0414   $77.04   $77.05   $77.00  
  7 purchase totals = $1,062.12       $1,170.0445   $1,170.04   $1,170.05   $1,170.00