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 $65.50   5.602%   $69.1693   $69.17   $69.15   $69.20  
  Purchase #2 $151.87   6.516%   $161.7658   $161.77   $161.75   $161.80  
  Purchase #3 $74.39   8.573%   $80.7675   $80.77   $80.75   $80.80  
  Purchase #4 $22.70   6.768%   $24.2363   $24.24   $24.25   $24.20  
  Purchase #5 $23.96   5.694%   $25.3243   $25.32   $25.30   $25.30  
  Purchase #6 $41.26   8.564%   $44.7935   $44.79   $44.80   $44.80  
  Purchase #7 $238.95   3.229%   $246.6657   $246.67   $246.65   $246.70  
  7 purchase totals = $618.63       $652.7224   $652.73   $652.65   $652.80