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 $241.59   11.653%   $269.7425   $269.74   $269.75   $269.70  
  Purchase #2 $52.60   11.835%   $58.8252   $58.83   $58.85   $58.80  
  Purchase #3 $231.29   6.384%   $246.0556   $246.06   $246.05   $246.10  
  Purchase #4 $75.61   11.278%   $84.1373   $84.14   $84.15   $84.10  
  Purchase #5 $96.39   8.766%   $104.8395   $104.84   $104.85   $104.80  
  Purchase #6 $223.43   9.521%   $244.7028   $244.70   $244.70   $244.70  
  Purchase #7 $13.61   6.747%   $14.5283   $14.53   $14.55   $14.50  
  7 purchase totals = $934.52       $1,022.8312   $1,022.84   $1,022.90   $1,022.70