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 $30.53   13.263%   $34.5792   $34.58   $34.60   $34.60  
  Purchase #2 $134.93   7.468%   $145.0066   $145.01   $145.00   $145.00  
  Purchase #3 $122.99   12.262%   $138.071   $138.07   $138.05   $138.10  
  Purchase #4 $109.41   10.181%   $120.549   $120.55   $120.55   $120.50  
  Purchase #5 $243.25   10.645%   $269.144   $269.14   $269.15   $269.10  
  Purchase #6 $159.96   13.666%   $181.8201   $181.82   $181.80   $181.80  
  Purchase #7 $234.44   12.542%   $263.8435   $263.84   $263.85   $263.80  
  7 purchase totals = $1,035.51       $1,153.0134   $1,153.01   $1,153.00   $1,152.90