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 $60.88   13.493%   $69.0945   $69.09   $69.10   $69.10  
  Purchase #2 $181.91   5.199%   $191.3675   $191.37   $191.35   $191.40  
  Purchase #3 $229.55   9.779%   $251.9977   $252.00   $252.00   $252.00  
  Purchase #4 $70.84   13.138%   $80.147   $80.15   $80.15   $80.10  
  Purchase #5 $110.86   4.107%   $115.413   $115.41   $115.40   $115.40  
  Purchase #6 $113.29   5.276%   $119.2672   $119.27   $119.25   $119.30  
  Purchase #7 $107.48   5.356%   $113.2366   $113.24   $113.25   $113.20  
  7 purchase totals = $874.81       $940.5235   $940.53   $940.50   $940.50