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 $35.37   6.196%   $37.5615   $37.56   $37.55   $37.60  
  Purchase #2 $235.25   4.795%   $246.5302   $246.53   $246.55   $246.50  
  Purchase #3 $86.95   11.791%   $97.2023   $97.20   $97.20   $97.20  
  Purchase #4 $33.41   3.241%   $34.4928   $34.49   $34.50   $34.50  
  Purchase #5 $126.29   6.558%   $134.5721   $134.57   $134.55   $134.60  
  Purchase #6 $183.49   10.206%   $202.217   $202.22   $202.20   $202.20  
  Purchase #7 $96.89   10.230%   $106.8018   $106.80   $106.80   $106.80  
  7 purchase totals = $797.65       $859.3777   $859.37   $859.35   $859.40