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 $62.67   12.544%   $70.5313   $70.53   $70.55   $70.50  
  Purchase #2 $188.25   12.279%   $211.3652   $211.37   $211.35   $211.40  
  Purchase #3 $189.51   6.864%   $202.518   $202.52   $202.50   $202.50  
  Purchase #4 $46.98   13.181%   $53.1724   $53.17   $53.15   $53.20  
  Purchase #5 $130.97   11.792%   $146.414   $146.41   $146.40   $146.40  
  Purchase #6 $226.36   9.692%   $248.2988   $248.30   $248.30   $248.30  
  Purchase #7 $22.73   7.569%   $24.4504   $24.45   $24.45   $24.50  
  7 purchase totals = $867.47       $956.7501   $956.75   $956.70   $956.80