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 $212.72   10.486%   $235.0258   $235.03   $235.05   $235.00  
  Purchase #2 $158.79   7.501%   $170.7008   $170.70   $170.70   $170.70  
  Purchase #3 $46.29   12.270%   $51.9698   $51.97   $51.95   $52.00  
  Purchase #4 $50.98   7.130%   $54.6149   $54.61   $54.60   $54.60  
  Purchase #5 $116.29   10.866%   $128.9261   $128.93   $128.95   $128.90  
  Purchase #6 $143.29   6.615%   $152.7686   $152.77   $152.75   $152.80  
  Purchase #7 $195.44   13.123%   $221.0876   $221.09   $221.10   $221.10  
  7 purchase totals = $923.80       $1,015.0936   $1,015.10   $1,015.10   $1,015.10