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 $168.95   8.146%   $182.7127   $182.71   $182.70   $182.70  
  Purchase #2 $53.69   11.159%   $59.6813   $59.68   $59.70   $59.70  
  Purchase #3 $215.45   9.495%   $235.907   $235.91   $235.90   $235.90  
  Purchase #4 $33.41   9.489%   $36.5803   $36.58   $36.60   $36.60  
  Purchase #5 $110.51   7.573%   $118.8789   $118.88   $118.90   $118.90  
  Purchase #6 $163.28   12.584%   $183.8272   $183.83   $183.85   $183.80  
  Purchase #7 $96.59   13.297%   $109.4336   $109.43   $109.45   $109.40  
  7 purchase totals = $841.88       $927.0210   $927.02   $927.10   $927.00