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 $180.53   12.265%   $202.672   $202.67   $202.65   $202.70  
  Purchase #2 $113.64   3.836%   $117.9992   $118.00   $118.00   $118.00  
  Purchase #3 $165.53   6.274%   $175.9154   $175.92   $175.90   $175.90  
  Purchase #4 $54.85   10.826%   $60.7881   $60.79   $60.80   $60.80  
  Purchase #5 $55.65   10.408%   $61.4421   $61.44   $61.45   $61.40  
  Purchase #6 $165.73   11.366%   $184.5669   $184.57   $184.55   $184.60  
  Purchase #7 $202.96   13.222%   $229.7954   $229.80   $229.80   $229.80  
  7 purchase totals = $938.89       $1,033.1791   $1,033.19   $1,033.15   $1,033.20