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 $58.35   9.236%   $63.7392   $63.74   $63.75   $63.70  
  Purchase #2 $117.41   9.561%   $128.6356   $128.64   $128.65   $128.60  
  Purchase #3 $25.38   4.417%   $26.501   $26.50   $26.50   $26.50  
  Purchase #4 $193.52   8.615%   $210.1917   $210.19   $210.20   $210.20  
  Purchase #5 $122.58   13.293%   $138.8746   $138.87   $138.85   $138.90  
  Purchase #6 $171.30   7.482%   $184.1167   $184.12   $184.10   $184.10  
  Purchase #7 $235.51   6.398%   $250.5779   $250.58   $250.60   $250.60  
  7 purchase totals = $924.05       $1,002.6367   $1,002.64   $1,002.65   $1,002.60