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 $36.65   13.328%   $41.5347   $41.53   $41.55   $41.50  
  Purchase #2 $110.98   3.126%   $114.4492   $114.45   $114.45   $114.40  
  Purchase #3 $100.31   4.773%   $105.0978   $105.10   $105.10   $105.10  
  Purchase #4 $75.37   8.279%   $81.6099   $81.61   $81.60   $81.60  
  Purchase #5 $221.61   4.794%   $232.234   $232.23   $232.25   $232.20  
  Purchase #6 $219.93   8.736%   $239.1431   $239.14   $239.15   $239.10  
  Purchase #7 $136.91   12.568%   $154.1168   $154.12   $154.10   $154.10  
  7 purchase totals = $901.76       $968.1855   $968.18   $968.20   $968.00