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 $63.45   13.301%   $71.8895   $71.89   $71.90   $71.90  
  Purchase #2 $150.95   10.602%   $166.9537   $166.95   $166.95   $167.00  
  Purchase #3 $127.77   4.126%   $133.0418   $133.04   $133.05   $133.00  
  Purchase #4 $206.37   12.846%   $232.8803   $232.88   $232.90   $232.90  
  Purchase #5 $130.48   13.316%   $147.8547   $147.85   $147.85   $147.90  
  Purchase #6 $145.80   3.756%   $151.2762   $151.28   $151.30   $151.30  
  Purchase #7 $190.26   7.336%   $204.2175   $204.22   $204.20   $204.20  
  7 purchase totals = $1,015.08       $1,108.1137   $1,108.11   $1,108.15   $1,108.20