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 $93.68   4.475%   $97.8722   $97.87   $97.85   $97.90  
  Purchase #2 $53.80   5.571%   $56.7972   $56.80   $56.80   $56.80  
  Purchase #3 $232.67   8.282%   $251.9397   $251.94   $251.95   $251.90  
  Purchase #4 $62.45   7.385%   $67.0619   $67.06   $67.05   $67.10  
  Purchase #5 $238.70   5.857%   $252.6807   $252.68   $252.70   $252.70  
  Purchase #6 $201.79   9.118%   $220.1892   $220.19   $220.20   $220.20  
  Purchase #7 $114.76   5.820%   $121.439   $121.44   $121.45   $121.40  
  7 purchase totals = $997.85       $1,067.9799   $1,067.98   $1,068.00   $1,068.00