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 $158.53   4.495%   $165.6559   $165.66   $165.65   $165.70  
  Purchase #2 $201.47   6.146%   $213.8523   $213.85   $213.85   $213.90  
  Purchase #3 $90.25   4.362%   $94.1867   $94.19   $94.20   $94.20  
  Purchase #4 $41.37   9.630%   $45.3539   $45.35   $45.35   $45.40  
  Purchase #5 $48.73   13.743%   $55.427   $55.43   $55.45   $55.40  
  Purchase #6 $59.77   5.392%   $62.9928   $62.99   $63.00   $63.00  
  Purchase #7 $56.62   4.585%   $59.216   $59.22   $59.20   $59.20  
  7 purchase totals = $656.74       $696.6846   $696.69   $696.70   $696.80