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 $83.39   13.251%   $94.44   $94.44   $94.45   $94.40  
  Purchase #2 $104.31   9.590%   $114.3133   $114.31   $114.30   $114.30  
  Purchase #3 $160.66   3.769%   $166.7153   $166.72   $166.70   $166.70  
  Purchase #4 $137.37   3.547%   $142.2425   $142.24   $142.25   $142.20  
  Purchase #5 $107.74   13.840%   $122.6512   $122.65   $122.65   $122.70  
  Purchase #6 $169.63   5.597%   $179.1242   $179.12   $179.10   $179.10  
  Purchase #7 $178.59   7.301%   $191.6289   $191.63   $191.65   $191.60  
  7 purchase totals = $941.69       $1,011.1154   $1,011.11   $1,011.10   $1,011.00