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 $29.83   11.481%   $33.2548   $33.25   $33.25   $33.30  
  Purchase #2 $124.83   10.521%   $137.9634   $137.96   $137.95   $138.00  
  Purchase #3 $236.40   4.701%   $247.5132   $247.51   $247.50   $247.50  
  Purchase #4 $170.37   13.300%   $193.0292   $193.03   $193.05   $193.00  
  Purchase #5 $52.94   3.772%   $54.9369   $54.94   $54.95   $54.90  
  Purchase #6 $210.50   4.520%   $220.0146   $220.01   $220.00   $220.00  
  Purchase #7 $133.71   3.444%   $138.315   $138.32   $138.30   $138.30  
  7 purchase totals = $958.58       $1,025.0271   $1,025.02   $1,025.00   $1,025.00