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 $132.62   13.869%   $151.0131   $151.01   $151.00   $151.00  
  Purchase #2 $114.83   10.211%   $126.5553   $126.56   $126.55   $126.60  
  Purchase #3 $29.77   11.343%   $33.1468   $33.15   $33.15   $33.10  
  Purchase #4 $246.98   12.480%   $277.8031   $277.80   $277.80   $277.80  
  Purchase #5 $104.59   13.515%   $118.7253   $118.73   $118.75   $118.70  
  Purchase #6 $167.56   12.214%   $188.0258   $188.03   $188.05   $188.00  
  Purchase #7 $128.57   11.689%   $143.5985   $143.60   $143.60   $143.60  
  7 purchase totals = $924.92       $1,038.8679   $1,038.88   $1,038.90   $1,038.80