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 $242.67   6.572%   $258.6183   $258.62   $258.60   $258.60  
  Purchase #2 $177.71   11.765%   $198.6176   $198.62   $198.60   $198.60  
  Purchase #3 $45.86   9.567%   $50.2474   $50.25   $50.25   $50.20  
  Purchase #4 $139.80   12.594%   $157.4064   $157.41   $157.40   $157.40  
  Purchase #5 $166.97   6.435%   $177.7145   $177.71   $177.70   $177.70  
  Purchase #6 $126.55   9.404%   $138.4508   $138.45   $138.45   $138.50  
  Purchase #7 $34.52   4.336%   $36.0168   $36.02   $36.00   $36.00  
  7 purchase totals = $934.08       $1,017.0718   $1,017.08   $1,017.00   $1,017.00