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 $72.53   4.766%   $75.9868   $75.99   $76.00   $76.00  
  Purchase #2 $177.96   13.632%   $202.2195   $202.22   $202.20   $202.20  
  Purchase #3 $214.99   4.399%   $224.4474   $224.45   $224.45   $224.40  
  Purchase #4 $213.29   4.823%   $223.577   $223.58   $223.60   $223.60  
  Purchase #5 $86.55   5.570%   $91.3708   $91.37   $91.35   $91.40  
  Purchase #6 $187.87   12.656%   $211.6468   $211.65   $211.65   $211.60  
  Purchase #7 $234.55   3.400%   $242.5247   $242.52   $242.50   $242.50  
  7 purchase totals = $1,187.74       $1,271.7730   $1,271.78   $1,271.75   $1,271.70