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 $204.86   8.251%   $221.763   $221.76   $221.75   $221.80  
  Purchase #2 $52.41   4.542%   $54.7905   $54.79   $54.80   $54.80  
  Purchase #3 $207.91   13.324%   $235.6119   $235.61   $235.60   $235.60  
  Purchase #4 $49.64   5.183%   $52.2128   $52.21   $52.20   $52.20  
  Purchase #5 $5.55   4.494%   $5.7994   $5.80   $5.80   $5.80  
  Purchase #6 $150.84   4.459%   $157.566   $157.57   $157.55   $157.60  
  Purchase #7 $218.84   3.285%   $226.0289   $226.03   $226.05   $226.00  
  7 purchase totals = $890.05       $953.7725   $953.77   $953.75   $953.80