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 $61.25   4.257%   $63.8574   $63.86   $63.85   $63.90  
  Purchase #2 $245.84   3.386%   $254.1641   $254.16   $254.15   $254.20  
  Purchase #3 $208.79   12.581%   $235.0579   $235.06   $235.05   $235.10  
  Purchase #4 $61.69   12.342%   $69.3038   $69.30   $69.30   $69.30  
  Purchase #5 $184.52   5.832%   $195.2812   $195.28   $195.30   $195.30  
  Purchase #6 $133.35   4.200%   $138.9507   $138.95   $138.95   $139.00  
  Purchase #7 $117.56   7.520%   $126.4005   $126.40   $126.40   $126.40  
  7 purchase totals = $1,013.00       $1,083.0156   $1,083.01   $1,083.00   $1,083.20