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 $122.71   9.479%   $134.3417   $134.34   $134.35   $134.30  
  Purchase #2 $225.42   6.599%   $240.2955   $240.30   $240.30   $240.30  
  Purchase #3 $167.42   6.115%   $177.6577   $177.66   $177.65   $177.70  
  Purchase #4 $40.44   7.642%   $43.5304   $43.53   $43.55   $43.50  
  Purchase #5 $147.50   5.119%   $155.0505   $155.05   $155.05   $155.10  
  Purchase #6 $36.77   11.233%   $40.9004   $40.90   $40.90   $40.90  
  Purchase #7 $207.43   4.384%   $216.5237   $216.52   $216.50   $216.50  
  7 purchase totals = $947.69       $1,008.2999   $1,008.30   $1,008.30   $1,008.30