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 $60.28   10.605%   $66.6727   $66.67   $66.65   $66.70  
  Purchase #2 $76.39   5.811%   $80.829   $80.83   $80.85   $80.80  
  Purchase #3 $61.33   7.373%   $65.8519   $65.85   $65.85   $65.90  
  Purchase #4 $213.49   6.244%   $226.8203   $226.82   $226.80   $226.80  
  Purchase #5 $50.78   11.231%   $56.4831   $56.48   $56.50   $56.50  
  Purchase #6 $166.32   5.392%   $175.288   $175.29   $175.30   $175.30  
  Purchase #7 $147.54   9.426%   $161.4471   $161.45   $161.45   $161.40  
  7 purchase totals = $776.13       $833.3921   $833.39   $833.40   $833.40