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 $227.87   11.157%   $253.2935   $253.29   $253.30   $253.30  
  Purchase #2 $181.46   8.216%   $196.3688   $196.37   $196.35   $196.40  
  Purchase #3 $202.45   6.367%   $215.34   $215.34   $215.35   $215.30  
  Purchase #4 $184.42   10.453%   $203.6974   $203.70   $203.70   $203.70  
  Purchase #5 $156.35   4.231%   $162.9652   $162.97   $162.95   $163.00  
  Purchase #6 $33.67   3.764%   $34.9373   $34.94   $34.95   $34.90  
  Purchase #7 $125.26   12.416%   $140.8123   $140.81   $140.80   $140.80  
  7 purchase totals = $1,111.48       $1,207.4145   $1,207.42   $1,207.40   $1,207.40