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 $58.89   11.356%   $65.5775   $65.58   $65.60   $65.60  
  Purchase #2 $149.45   12.113%   $167.5529   $167.55   $167.55   $167.60  
  Purchase #3 $248.83   4.658%   $260.4205   $260.42   $260.40   $260.40  
  Purchase #4 $233.31   9.276%   $254.9518   $254.95   $254.95   $255.00  
  Purchase #5 $173.30   6.242%   $184.1174   $184.12   $184.10   $184.10  
  Purchase #6 $169.34   8.417%   $183.5933   $183.59   $183.60   $183.60  
  Purchase #7 $202.85   13.594%   $230.4254   $230.43   $230.45   $230.40  
  7 purchase totals = $1,235.97       $1,346.6388   $1,346.64   $1,346.65   $1,346.70