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 $205.95   9.259%   $225.0189   $225.02   $225.00   $225.00  
  Purchase #2 $214.99   11.367%   $239.4279   $239.43   $239.45   $239.40  
  Purchase #3 $24.35   9.668%   $26.7042   $26.70   $26.70   $26.70  
  Purchase #4 $137.59   12.771%   $155.1616   $155.16   $155.15   $155.20  
  Purchase #5 $133.53   6.306%   $141.9504   $141.95   $141.95   $142.00  
  Purchase #6 $123.91   8.169%   $134.0322   $134.03   $134.05   $134.00  
  Purchase #7 $109.72   10.753%   $121.5182   $121.52   $121.50   $121.50  
  7 purchase totals = $950.04       $1,043.8134   $1,043.81   $1,043.80   $1,043.80