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 $88.62   12.614%   $99.7985   $99.80   $99.80   $99.80  
  Purchase #2 $227.62   10.591%   $251.7272   $251.73   $251.75   $251.70  
  Purchase #3 $72.56   10.420%   $80.1208   $80.12   $80.10   $80.10  
  Purchase #4 $169.40   8.424%   $183.6703   $183.67   $183.65   $183.70  
  Purchase #5 $124.85   3.749%   $129.5306   $129.53   $129.55   $129.50  
  Purchase #6 $203.40   3.801%   $211.1312   $211.13   $211.15   $211.10  
  Purchase #7 $50.84   7.844%   $54.8279   $54.83   $54.85   $54.80  
  7 purchase totals = $937.29       $1,010.8065   $1,010.81   $1,010.85   $1,010.70