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 $47.97   8.711%   $52.1487   $52.15   $52.15   $52.10  
  Purchase #2 $223.60   5.259%   $235.3591   $235.36   $235.35   $235.40  
  Purchase #3 $194.44   12.259%   $218.2764   $218.28   $218.30   $218.30  
  Purchase #4 $156.41   13.317%   $177.2391   $177.24   $177.25   $177.20  
  Purchase #5 $97.25   10.690%   $107.646   $107.65   $107.65   $107.60  
  Purchase #6 $148.85   5.611%   $157.202   $157.20   $157.20   $157.20  
  Purchase #7 $223.68   13.415%   $253.6867   $253.69   $253.70   $253.70  
  7 purchase totals = $1,092.20       $1,201.5580   $1,201.57   $1,201.60   $1,201.50