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 $85.75   10.867%   $95.0685   $95.07   $95.05   $95.10  
  Purchase #2 $69.65   11.591%   $77.7231   $77.72   $77.70   $77.70  
  Purchase #3 $108.77   4.481%   $113.644   $113.64   $113.65   $113.60  
  Purchase #4 $154.87   9.208%   $169.1304   $169.13   $169.15   $169.10  
  Purchase #5 $99.49   7.820%   $107.2701   $107.27   $107.25   $107.30  
  Purchase #6 $193.75   6.410%   $206.1694   $206.17   $206.15   $206.20  
  Purchase #7 $27.50   5.480%   $29.007   $29.01   $29.00   $29.00  
  7 purchase totals = $739.78       $798.0125   $798.01   $797.95   $798.00