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 $148.59   4.819%   $155.7506   $155.75   $155.75   $155.80  
  Purchase #2 $23.55   9.348%   $25.7515   $25.75   $25.75   $25.80  
  Purchase #3 $128.37   3.654%   $133.0606   $133.06   $133.05   $133.10  
  Purchase #4 $222.72   5.123%   $234.1299   $234.13   $234.15   $234.10  
  Purchase #5 $84.87   7.515%   $91.248   $91.25   $91.25   $91.20  
  Purchase #6 $162.60   4.426%   $169.7967   $169.80   $169.80   $169.80  
  Purchase #7 $114.79   6.690%   $122.4695   $122.47   $122.45   $122.50  
  7 purchase totals = $885.49       $932.2068   $932.21   $932.20   $932.30