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 $75.94   3.569%   $78.6503   $78.65   $78.65   $78.70  
  Purchase #2 $52.43   11.259%   $58.3331   $58.33   $58.35   $58.30  
  Purchase #3 $226.59   11.351%   $252.3102   $252.31   $252.30   $252.30  
  Purchase #4 $53.69   13.449%   $60.9108   $60.91   $60.90   $60.90  
  Purchase #5 $237.29   4.181%   $247.2111   $247.21   $247.20   $247.20  
  Purchase #6 $90.69   3.469%   $93.836   $93.84   $93.85   $93.80  
  Purchase #7 $239.50   11.133%   $266.1635   $266.16   $266.15   $266.20  
  7 purchase totals = $976.13       $1,057.4150   $1,057.41   $1,057.40   $1,057.40