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 $23.58   3.696%   $24.4515   $24.45   $24.45   $24.50  
  Purchase #2 $175.77   12.424%   $197.6077   $197.61   $197.60   $197.60  
  Purchase #3 $41.81   6.776%   $44.643   $44.64   $44.65   $44.60  
  Purchase #4 $211.88   9.481%   $231.9683   $231.97   $231.95   $232.00  
  Purchase #5 $236.83   7.711%   $255.092   $255.09   $255.10   $255.10  
  Purchase #6 $89.47   9.758%   $98.2005   $98.20   $98.20   $98.20  
  Purchase #7 $201.79   5.221%   $212.3255   $212.33   $212.35   $212.30  
  7 purchase totals = $981.13       $1,064.2885   $1,064.29   $1,064.30   $1,064.30