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 $68.95   9.526%   $75.5182   $75.52   $75.50   $75.50  
  Purchase #2 $48.74   3.866%   $50.6243   $50.62   $50.60   $50.60  
  Purchase #3 $230.58   13.723%   $262.2225   $262.22   $262.20   $262.20  
  Purchase #4 $203.59   13.744%   $231.5714   $231.57   $231.55   $231.60  
  Purchase #5 $173.41   11.502%   $193.3556   $193.36   $193.35   $193.40  
  Purchase #6 $226.84   6.322%   $241.1808   $241.18   $241.20   $241.20  
  Purchase #7 $240.44   9.253%   $262.6879   $262.69   $262.70   $262.70  
  7 purchase totals = $1,192.55       $1,317.1607   $1,317.16   $1,317.10   $1,317.20