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 $186.33   8.270%   $201.7395   $201.74   $201.75   $201.70  
  Purchase #2 $49.25   11.220%   $54.7759   $54.78   $54.80   $54.80  
  Purchase #3 $155.82   12.753%   $175.6917   $175.69   $175.70   $175.70  
  Purchase #4 $113.67   7.730%   $122.4567   $122.46   $122.45   $122.50  
  Purchase #5 $107.82   12.794%   $121.6145   $121.61   $121.60   $121.60  
  Purchase #6 $166.90   9.701%   $183.091   $183.09   $183.10   $183.10  
  Purchase #7 $222.54   11.810%   $248.822   $248.82   $248.80   $248.80  
  7 purchase totals = $1,002.33       $1,108.1913   $1,108.19   $1,108.20   $1,108.20