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 $73.59   12.797%   $83.0073   $83.01   $83.00   $83.00  
  Purchase #2 $220.91   6.488%   $235.2426   $235.24   $235.25   $235.20  
  Purchase #3 $209.34   6.370%   $222.675   $222.68   $222.70   $222.70  
  Purchase #4 $98.68   7.485%   $106.0662   $106.07   $106.05   $106.10  
  Purchase #5 $177.82   5.447%   $187.5059   $187.51   $187.50   $187.50  
  Purchase #6 $166.46   4.718%   $174.3136   $174.31   $174.30   $174.30  
  Purchase #7 $38.42   5.789%   $40.6441   $40.64   $40.65   $40.60  
  7 purchase totals = $985.22       $1,049.4547   $1,049.46   $1,049.45   $1,049.40