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 $60.80   4.572%   $63.5798   $63.58   $63.60   $63.60  
  Purchase #2 $22.78   13.261%   $25.8009   $25.80   $25.80   $25.80  
  Purchase #3 $238.53   11.862%   $266.8244   $266.82   $266.80   $266.80  
  Purchase #4 $156.99   9.696%   $172.2118   $172.21   $172.20   $172.20  
  Purchase #5 $151.45   11.791%   $169.3075   $169.31   $169.30   $169.30  
  Purchase #6 $177.80   3.591%   $184.1848   $184.18   $184.20   $184.20  
  Purchase #7 $38.80   11.667%   $43.3268   $43.33   $43.35   $43.30  
  7 purchase totals = $847.15       $925.2360   $925.23   $925.25   $925.20