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 $233.39   13.342%   $264.5289   $264.53   $264.55   $264.50  
  Purchase #2 $108.93   6.816%   $116.3547   $116.35   $116.35   $116.40  
  Purchase #3 $80.54   11.250%   $89.6008   $89.60   $89.60   $89.60  
  Purchase #4 $187.99   7.760%   $202.578   $202.58   $202.60   $202.60  
  Purchase #5 $147.65   12.550%   $166.1801   $166.18   $166.20   $166.20  
  Purchase #6 $10.77   7.863%   $11.6168   $11.62   $11.60   $11.60  
  Purchase #7 $221.96   13.846%   $252.6926   $252.69   $252.70   $252.70  
  7 purchase totals = $991.23       $1,103.5519   $1,103.55   $1,103.60   $1,103.60