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 $60.94   8.329%   $66.0157   $66.02   $66.00   $66.00  
  Purchase #2 $162.78   8.827%   $177.1486   $177.15   $177.15   $177.10  
  Purchase #3 $165.39   3.347%   $170.9256   $170.93   $170.95   $170.90  
  Purchase #4 $121.59   8.244%   $131.6139   $131.61   $131.60   $131.60  
  Purchase #5 $193.62   9.728%   $212.4554   $212.46   $212.45   $212.50  
  Purchase #6 $239.50   3.494%   $247.8681   $247.87   $247.85   $247.90  
  Purchase #7 $129.54   12.253%   $145.4125   $145.41   $145.40   $145.40  
  7 purchase totals = $1,073.36       $1,151.4398   $1,151.45   $1,151.40   $1,151.40