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 $152.30   7.817%   $164.2053   $164.21   $164.20   $164.20  
  Purchase #2 $24.25   6.383%   $25.7979   $25.80   $25.80   $25.80  
  Purchase #3 $49.67   6.823%   $53.059   $53.06   $53.05   $53.10  
  Purchase #4 $43.60   7.436%   $46.8421   $46.84   $46.85   $46.80  
  Purchase #5 $102.55   12.508%   $115.377   $115.38   $115.40   $115.40  
  Purchase #6 $165.41   13.582%   $187.876   $187.88   $187.90   $187.90  
  Purchase #7 $174.85   11.234%   $194.4926   $194.49   $194.50   $194.50  
  7 purchase totals = $712.63       $787.6499   $787.66   $787.70   $787.70