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 $245.28   11.132%   $272.5846   $272.58   $272.60   $272.60  
  Purchase #2 $181.73   8.223%   $196.6737   $196.67   $196.65   $196.70  
  Purchase #3 $7.58   8.823%   $8.2488   $8.25   $8.25   $8.20  
  Purchase #4 $167.33   5.163%   $175.9692   $175.97   $175.95   $176.00  
  Purchase #5 $15.69   5.299%   $16.5214   $16.52   $16.50   $16.50  
  Purchase #6 $128.66   8.117%   $139.1033   $139.10   $139.10   $139.10  
  Purchase #7 $167.65   13.155%   $189.7044   $189.70   $189.70   $189.70  
  7 purchase totals = $913.92       $998.8054   $998.79   $998.75   $998.80