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 $168.54   13.315%   $190.9811   $190.98   $191.00   $191.00  
  Purchase #2 $62.45   3.816%   $64.8331   $64.83   $64.85   $64.80  
  Purchase #3 $158.67   11.721%   $177.2677   $177.27   $177.25   $177.30  
  Purchase #4 $129.85   13.651%   $147.5758   $147.58   $147.60   $147.60  
  Purchase #5 $173.82   6.635%   $185.353   $185.35   $185.35   $185.40  
  Purchase #6 $154.54   8.579%   $167.798   $167.80   $167.80   $167.80  
  Purchase #7 $197.54   11.534%   $220.3243   $220.32   $220.30   $220.30  
  7 purchase totals = $1,045.41       $1,154.1330   $1,154.13   $1,154.15   $1,154.20