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 $209.87   11.152%   $233.2747   $233.27   $233.25   $233.30  
  Purchase #2 $56.47   12.336%   $63.4361   $63.44   $63.45   $63.40  
  Purchase #3 $202.38   10.605%   $223.8424   $223.84   $223.85   $223.80  
  Purchase #4 $176.30   12.476%   $198.2952   $198.30   $198.30   $198.30  
  Purchase #5 $206.27   10.737%   $228.4172   $228.42   $228.40   $228.40  
  Purchase #6 $20.37   8.353%   $22.0715   $22.07   $22.05   $22.10  
  Purchase #7 $88.33   12.689%   $99.5382   $99.54   $99.55   $99.50  
  7 purchase totals = $959.99       $1,068.8753   $1,068.88   $1,068.85   $1,068.80