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 $66.47   6.207%   $70.5958   $70.60   $70.60   $70.60  
  Purchase #2 $235.50   4.735%   $246.6509   $246.65   $246.65   $246.70  
  Purchase #3 $217.40   3.369%   $224.7242   $224.72   $224.70   $224.70  
  Purchase #4 $145.32   6.528%   $154.8065   $154.81   $154.80   $154.80  
  Purchase #5 $192.98   13.743%   $219.5012   $219.50   $219.50   $219.50  
  Purchase #6 $147.52   8.475%   $160.0223   $160.02   $160.00   $160.00  
  Purchase #7 $241.62   11.469%   $269.3314   $269.33   $269.35   $269.30  
  7 purchase totals = $1,246.81       $1,345.6323   $1,345.63   $1,345.60   $1,345.60