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 $184.62   10.313%   $203.6599   $203.66   $203.65   $203.70  
  Purchase #2 $173.69   4.664%   $181.7909   $181.79   $181.80   $181.80  
  Purchase #3 $49.33   5.432%   $52.0096   $52.01   $52.00   $52.00  
  Purchase #4 $38.70   8.761%   $42.0905   $42.09   $42.10   $42.10  
  Purchase #5 $167.30   7.640%   $180.0817   $180.08   $180.10   $180.10  
  Purchase #6 $191.25   4.107%   $199.1046   $199.10   $199.10   $199.10  
  Purchase #7 $63.63   8.460%   $69.0131   $69.01   $69.00   $69.00  
  7 purchase totals = $868.52       $927.7503   $927.74   $927.75   $927.80