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 $153.86   8.353%   $166.7119   $166.71   $166.70   $166.70  
  Purchase #2 $131.62   13.534%   $149.4335   $149.43   $149.45   $149.40  
  Purchase #3 $161.90   5.649%   $171.0457   $171.05   $171.05   $171.00  
  Purchase #4 $16.53   8.146%   $17.8765   $17.88   $17.90   $17.90  
  Purchase #5 $170.85   7.578%   $183.797   $183.80   $183.80   $183.80  
  Purchase #6 $113.64   11.862%   $127.12   $127.12   $127.10   $127.10  
  Purchase #7 $55.79   4.383%   $58.2353   $58.24   $58.25   $58.20  
  7 purchase totals = $804.19       $874.2199   $874.23   $874.25   $874.10