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 $186.86   8.276%   $202.3245   $202.32   $202.30   $202.30  
  Purchase #2 $224.29   4.852%   $235.1726   $235.17   $235.15   $235.20  
  Purchase #3 $197.64   9.391%   $216.2004   $216.20   $216.20   $216.20  
  Purchase #4 $149.57   4.148%   $155.7742   $155.77   $155.75   $155.80  
  Purchase #5 $42.35   4.783%   $44.3756   $44.38   $44.40   $44.40  
  Purchase #6 $138.55   9.586%   $151.8314   $151.83   $151.85   $151.80  
  Purchase #7 $36.45   5.723%   $38.536   $38.54   $38.55   $38.50  
  7 purchase totals = $975.71       $1,044.2147   $1,044.21   $1,044.20   $1,044.20