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 $238.77   12.642%   $268.9553   $268.96   $268.95   $269.00  
  Purchase #2 $151.93   10.434%   $167.7824   $167.78   $167.80   $167.80  
  Purchase #3 $105.77   9.488%   $115.8055   $115.81   $115.80   $115.80  
  Purchase #4 $62.58   13.117%   $70.7886   $70.79   $70.80   $70.80  
  Purchase #5 $18.50   4.829%   $19.3934   $19.39   $19.40   $19.40  
  Purchase #6 $31.58   8.613%   $34.3   $34.30   $34.30   $34.30  
  Purchase #7 $223.74   11.740%   $250.0071   $250.01   $250.00   $250.00  
  7 purchase totals = $832.87       $927.0323   $927.04   $927.05   $927.10