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 $205.64   6.502%   $219.0107   $219.01   $219.00   $219.00  
  Purchase #2 $181.96   13.218%   $206.0115   $206.01   $206.00   $206.00  
  Purchase #3 $155.96   3.359%   $161.1987   $161.20   $161.20   $161.20  
  Purchase #4 $108.54   9.593%   $118.9522   $118.95   $118.95   $119.00  
  Purchase #5 $41.57   6.333%   $44.2026   $44.20   $44.20   $44.20  
  Purchase #6 $157.28   12.745%   $177.3253   $177.33   $177.35   $177.30  
  Purchase #7 $228.61   4.845%   $239.6862   $239.69   $239.70   $239.70  
  7 purchase totals = $1,079.56       $1,166.3872   $1,166.39   $1,166.40   $1,166.40