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 $212.61   6.418%   $226.2553   $226.26   $226.25   $226.30  
  Purchase #2 $159.86   3.749%   $165.8532   $165.85   $165.85   $165.90  
  Purchase #3 $52.42   11.254%   $58.3193   $58.32   $58.30   $58.30  
  Purchase #4 $122.83   9.661%   $134.6966   $134.70   $134.70   $134.70  
  Purchase #5 $223.92   6.140%   $237.6687   $237.67   $237.65   $237.70  
  Purchase #6 $89.36   11.827%   $99.9286   $99.93   $99.95   $99.90  
  Purchase #7 $248.53   4.529%   $259.7859   $259.79   $259.80   $259.80  
  7 purchase totals = $1,109.53       $1,182.5076   $1,182.52   $1,182.50   $1,182.60