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 $60.40   13.748%   $68.7038   $68.70   $68.70   $68.70  
  Purchase #2 $240.62   5.732%   $254.4123   $254.41   $254.40   $254.40  
  Purchase #3 $58.35   10.758%   $64.6273   $64.63   $64.65   $64.60  
  Purchase #4 $229.88   6.439%   $244.682   $244.68   $244.70   $244.70  
  Purchase #5 $192.64   5.789%   $203.7919   $203.79   $203.80   $203.80  
  Purchase #6 $32.73   11.801%   $36.5925   $36.59   $36.60   $36.60  
  Purchase #7 $62.79   8.479%   $68.114   $68.11   $68.10   $68.10  
  7 purchase totals = $877.41       $940.9238   $940.91   $940.95   $940.90