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 $67.58   12.845%   $76.2607   $76.26   $76.25   $76.30  
  Purchase #2 $185.52   9.119%   $202.4376   $202.44   $202.45   $202.40  
  Purchase #3 $206.72   9.676%   $226.7222   $226.72   $226.70   $226.70  
  Purchase #4 $24.85   5.353%   $26.1802   $26.18   $26.20   $26.20  
  Purchase #5 $148.73   5.552%   $156.9875   $156.99   $157.00   $157.00  
  Purchase #6 $107.58   3.123%   $110.9397   $110.94   $110.95   $110.90  
  Purchase #7 $247.28   4.140%   $257.5174   $257.52   $257.50   $257.50  
  7 purchase totals = $988.26       $1,057.0453   $1,057.05   $1,057.05   $1,057.00