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 $87.35   10.533%   $96.5506   $96.55   $96.55   $96.60  
  Purchase #2 $51.71   8.203%   $55.9518   $55.95   $55.95   $56.00  
  Purchase #3 $110.27   4.627%   $115.3722   $115.37   $115.35   $115.40  
  Purchase #4 $147.76   12.312%   $165.9522   $165.95   $165.95   $166.00  
  Purchase #5 $92.36   13.309%   $104.6522   $104.65   $104.65   $104.70  
  Purchase #6 $148.58   13.292%   $168.3293   $168.33   $168.35   $168.30  
  Purchase #7 $64.25   5.618%   $67.8596   $67.86   $67.85   $67.90  
  7 purchase totals = $702.28       $774.6679   $774.66   $774.65   $774.90