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 $11.31   12.716%   $12.7482   $12.75   $12.75   $12.70  
  Purchase #2 $70.74   5.634%   $74.7255   $74.73   $74.75   $74.70  
  Purchase #3 $219.82   9.849%   $241.4701   $241.47   $241.45   $241.50  
  Purchase #4 $115.91   13.463%   $131.515   $131.52   $131.50   $131.50  
  Purchase #5 $95.93   13.712%   $109.0839   $109.08   $109.10   $109.10  
  Purchase #6 $157.26   3.746%   $163.151   $163.15   $163.15   $163.20  
  Purchase #7 $105.76   13.472%   $120.008   $120.01   $120.00   $120.00  
  7 purchase totals = $776.73       $852.7017   $852.71   $852.70   $852.70