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 $166.38   11.538%   $185.5769   $185.58   $185.60   $185.60  
  Purchase #2 $22.30   10.771%   $24.7019   $24.70   $24.70   $24.70  
  Purchase #3 $153.84   11.125%   $170.9547   $170.95   $170.95   $171.00  
  Purchase #4 $81.87   12.392%   $92.0153   $92.02   $92.00   $92.00  
  Purchase #5 $245.84   3.263%   $253.8618   $253.86   $253.85   $253.90  
  Purchase #6 $204.71   10.701%   $226.616   $226.62   $226.60   $226.60  
  Purchase #7 $77.45   9.484%   $84.7954   $84.80   $84.80   $84.80  
  7 purchase totals = $952.39       $1,038.5220   $1,038.53   $1,038.50   $1,038.60