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 $226.49   6.756%   $241.7917   $241.79   $241.80   $241.80  
  Purchase #2 $53.94   4.395%   $56.3107   $56.31   $56.30   $56.30  
  Purchase #3 $189.93   6.565%   $202.3989   $202.40   $202.40   $202.40  
  Purchase #4 $234.64   3.589%   $243.0612   $243.06   $243.05   $243.10  
  Purchase #5 $169.64   11.573%   $189.2724   $189.27   $189.25   $189.30  
  Purchase #6 $223.82   7.186%   $239.9037   $239.90   $239.90   $239.90  
  Purchase #7 $15.52   5.416%   $16.3606   $16.36   $16.35   $16.40  
  7 purchase totals = $1,113.98       $1,189.0992   $1,189.09   $1,189.05   $1,189.20