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 $106.71   11.255%   $118.7202   $118.72   $118.70   $118.70  
  Purchase #2 $53.52   12.298%   $60.1019   $60.10   $60.10   $60.10  
  Purchase #3 $224.68   11.673%   $250.9069   $250.91   $250.90   $250.90  
  Purchase #4 $136.90   10.585%   $151.3909   $151.39   $151.40   $151.40  
  Purchase #5 $238.80   5.704%   $252.4212   $252.42   $252.40   $252.40  
  Purchase #6 $102.32   8.350%   $110.8637   $110.86   $110.85   $110.90  
  Purchase #7 $162.31   6.577%   $172.9851   $172.99   $173.00   $173.00  
  7 purchase totals = $1,025.24       $1,117.3899   $1,117.39   $1,117.35   $1,117.40