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 $194.96   8.232%   $211.0091   $211.01   $211.00   $211.00  
  Purchase #2 $150.67   3.218%   $155.5186   $155.52   $155.50   $155.50  
  Purchase #3 $10.84   11.702%   $12.1085   $12.11   $12.10   $12.10  
  Purchase #4 $20.58   8.103%   $22.2476   $22.25   $22.25   $22.20  
  Purchase #5 $141.64   8.675%   $153.9273   $153.93   $153.95   $153.90  
  Purchase #6 $209.54   9.688%   $229.8402   $229.84   $229.85   $229.80  
  Purchase #7 $216.63   4.397%   $226.1552   $226.16   $226.15   $226.20  
  7 purchase totals = $944.86       $1,010.8065   $1,010.82   $1,010.80   $1,010.70