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 $181.96   5.362%   $191.7167   $191.72   $191.70   $191.70  
  Purchase #2 $217.89   6.421%   $231.8807   $231.88   $231.90   $231.90  
  Purchase #3 $194.32   11.150%   $215.9867   $215.99   $216.00   $216.00  
  Purchase #4 $246.58   7.643%   $265.4261   $265.43   $265.45   $265.40  
  Purchase #5 $211.36   9.609%   $231.6696   $231.67   $231.65   $231.70  
  Purchase #6 $179.35   10.573%   $198.3127   $198.31   $198.30   $198.30  
  Purchase #7 $162.69   6.228%   $172.8223   $172.82   $172.80   $172.80  
  7 purchase totals = $1,394.15       $1,507.8148   $1,507.82   $1,507.80   $1,507.80