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 $24.68   13.681%   $28.0565   $28.06   $28.05   $28.10  
  Purchase #2 $118.67   11.873%   $132.7597   $132.76   $132.75   $132.80  
  Purchase #3 $212.58   3.424%   $219.8587   $219.86   $219.85   $219.90  
  Purchase #4 $189.88   6.119%   $201.4988   $201.50   $201.50   $201.50  
  Purchase #5 $189.95   13.625%   $215.8307   $215.83   $215.85   $215.80  
  Purchase #6 $147.60   6.185%   $156.7291   $156.73   $156.75   $156.70  
  Purchase #7 $165.84   13.773%   $188.6811   $188.68   $188.70   $188.70  
  7 purchase totals = $1,049.20       $1,143.4146   $1,143.42   $1,143.45   $1,143.50