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 $232.79   12.523%   $261.9423   $261.94   $261.95   $261.90  
  Purchase #2 $56.91   11.485%   $63.4461   $63.45   $63.45   $63.40  
  Purchase #3 $49.93   9.789%   $54.8176   $54.82   $54.80   $54.80  
  Purchase #4 $229.59   9.535%   $251.4814   $251.48   $251.50   $251.50  
  Purchase #5 $160.76   11.442%   $179.1542   $179.15   $179.15   $179.20  
  Purchase #6 $77.37   5.145%   $81.3507   $81.35   $81.35   $81.40  
  Purchase #7 $117.70   13.746%   $133.879   $133.88   $133.90   $133.90  
  7 purchase totals = $925.05       $1,026.0713   $1,026.07   $1,026.10   $1,026.10