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 $92.40   12.160%   $103.6358   $103.64   $103.65   $103.60  
  Purchase #2 $167.91   4.307%   $175.1419   $175.14   $175.15   $175.10  
  Purchase #3 $214.65   6.320%   $228.2159   $228.22   $228.20   $228.20  
  Purchase #4 $66.57   10.691%   $73.687   $73.69   $73.70   $73.70  
  Purchase #5 $124.78   12.280%   $140.103   $140.10   $140.10   $140.10  
  Purchase #6 $152.59   7.187%   $163.5566   $163.56   $163.55   $163.60  
  Purchase #7 $196.95   6.166%   $209.0939   $209.09   $209.10   $209.10  
  7 purchase totals = $1,015.85       $1,093.4341   $1,093.44   $1,093.45   $1,093.40