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 $94.37   7.183%   $101.1486   $101.15   $101.15   $101.10  
  Purchase #2 $179.99   8.150%   $194.6592   $194.66   $194.65   $194.70  
  Purchase #3 $206.47   10.675%   $228.5107   $228.51   $228.50   $228.50  
  Purchase #4 $235.41   9.308%   $257.322   $257.32   $257.30   $257.30  
  Purchase #5 $58.82   11.654%   $65.6749   $65.67   $65.65   $65.70  
  Purchase #6 $172.52   6.625%   $183.9495   $183.95   $183.95   $183.90  
  Purchase #7 $76.73   11.365%   $85.4504   $85.45   $85.45   $85.50  
  7 purchase totals = $1,024.31       $1,116.7153   $1,116.71   $1,116.65   $1,116.70