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 $94.64   12.619%   $106.5826   $106.58   $106.60   $106.60  
  Purchase #2 $33.86   4.259%   $35.3021   $35.30   $35.30   $35.30  
  Purchase #3 $32.57   9.174%   $35.558   $35.56   $35.55   $35.60  
  Purchase #4 $219.75   6.746%   $234.5743   $234.57   $234.55   $234.60  
  Purchase #5 $100.80   6.710%   $107.5637   $107.56   $107.55   $107.60  
  Purchase #6 $47.93   12.114%   $53.7362   $53.74   $53.75   $53.70  
  Purchase #7 $118.57   4.869%   $124.3432   $124.34   $124.35   $124.30  
  7 purchase totals = $648.12       $697.6601   $697.65   $697.65   $697.70