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 $187.98   7.392%   $201.8755   $201.88   $201.90   $201.90  
  Purchase #2 $95.33   4.552%   $99.6694   $99.67   $99.65   $99.70  
  Purchase #3 $55.44   12.185%   $62.1954   $62.20   $62.20   $62.20  
  Purchase #4 $85.98   5.341%   $90.5722   $90.57   $90.55   $90.60  
  Purchase #5 $208.64   13.855%   $237.5471   $237.55   $237.55   $237.50  
  Purchase #6 $225.96   4.367%   $235.8277   $235.83   $235.85   $235.80  
  Purchase #7 $93.32   6.304%   $99.2029   $99.20   $99.20   $99.20  
  7 purchase totals = $952.65       $1,026.8902   $1,026.90   $1,026.90   $1,026.90