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 $236.26   9.642%   $259.0402   $259.04   $259.05   $259.00  
  Purchase #2 $138.95   9.626%   $152.3253   $152.33   $152.35   $152.30  
  Purchase #3 $120.91   11.539%   $134.8618   $134.86   $134.85   $134.90  
  Purchase #4 $32.51   6.133%   $34.5038   $34.50   $34.50   $34.50  
  Purchase #5 $91.53   12.176%   $102.6747   $102.67   $102.65   $102.70  
  Purchase #6 $165.73   4.446%   $173.0984   $173.10   $173.10   $173.10  
  Purchase #7 $87.48   8.772%   $95.1537   $95.15   $95.15   $95.20  
  7 purchase totals = $873.37       $951.6579   $951.65   $951.65   $951.70