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 $206.62   12.288%   $232.0095   $232.01   $232.00   $232.00  
  Purchase #2 $161.82   11.659%   $180.6866   $180.69   $180.70   $180.70  
  Purchase #3 $189.50   4.581%   $198.181   $198.18   $198.20   $198.20  
  Purchase #4 $113.61   12.789%   $128.1396   $128.14   $128.15   $128.10  
  Purchase #5 $25.29   3.201%   $26.0995   $26.10   $26.10   $26.10  
  Purchase #6 $132.65   5.130%   $139.4549   $139.45   $139.45   $139.50  
  Purchase #7 $96.64   7.166%   $103.5652   $103.57   $103.55   $103.60  
  7 purchase totals = $926.13       $1,008.1363   $1,008.14   $1,008.15   $1,008.20