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 $48.90   11.173%   $54.3636   $54.36   $54.35   $54.40  
  Purchase #2 $181.43   5.798%   $191.9493   $191.95   $191.95   $191.90  
  Purchase #3 $177.46   13.377%   $201.1988   $201.20   $201.20   $201.20  
  Purchase #4 $159.72   4.289%   $166.5704   $166.57   $166.55   $166.60  
  Purchase #5 $217.68   8.246%   $235.6299   $235.63   $235.65   $235.60  
  Purchase #6 $223.91   13.484%   $254.102   $254.10   $254.10   $254.10  
  Purchase #7 $33.92   8.809%   $36.908   $36.91   $36.90   $36.90  
  7 purchase totals = $1,043.02       $1,140.7220   $1,140.72   $1,140.70   $1,140.70