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 $11.66   7.679%   $12.5554   $12.56   $12.55   $12.60  
  Purchase #2 $200.56   8.109%   $216.8234   $216.82   $216.80   $216.80  
  Purchase #3 $176.49   12.584%   $198.6995   $198.70   $198.70   $198.70  
  Purchase #4 $54.74   9.839%   $60.1259   $60.13   $60.15   $60.10  
  Purchase #5 $166.94   10.550%   $184.5522   $184.55   $184.55   $184.60  
  Purchase #6 $247.42   6.242%   $262.864   $262.86   $262.85   $262.90  
  Purchase #7 $80.52   5.365%   $84.8399   $84.84   $84.85   $84.80  
  7 purchase totals = $938.33       $1,020.4603   $1,020.46   $1,020.45   $1,020.50