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 $207.35   13.358%   $235.0478   $235.05   $235.05   $235.00  
  Purchase #2 $142.58   9.871%   $156.6541   $156.65   $156.65   $156.70  
  Purchase #3 $156.40   9.112%   $170.6512   $170.65   $170.65   $170.70  
  Purchase #4 $21.88   10.532%   $24.1844   $24.18   $24.20   $24.20  
  Purchase #5 $197.76   12.745%   $222.9645   $222.96   $222.95   $223.00  
  Purchase #6 $99.77   7.689%   $107.4413   $107.44   $107.45   $107.40  
  Purchase #7 $158.80   5.414%   $167.3974   $167.40   $167.40   $167.40  
  7 purchase totals = $984.54       $1,084.3407   $1,084.33   $1,084.35   $1,084.40