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 $88.36   9.317%   $96.5925   $96.59   $96.60   $96.60  
  Purchase #2 $53.73   8.190%   $58.1305   $58.13   $58.15   $58.10  
  Purchase #3 $22.87   8.329%   $24.7748   $24.77   $24.75   $24.80  
  Purchase #4 $209.61   7.294%   $224.899   $224.90   $224.90   $224.90  
  Purchase #5 $127.93   12.817%   $144.3268   $144.33   $144.35   $144.30  
  Purchase #6 $217.34   6.744%   $231.9974   $232.00   $232.00   $232.00  
  Purchase #7 $43.40   3.746%   $45.0258   $45.03   $45.05   $45.00  
  7 purchase totals = $763.24       $825.7468   $825.75   $825.80   $825.70