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 $156.94   12.562%   $176.6548   $176.65   $176.65   $176.70  
  Purchase #2 $36.37   4.620%   $38.0503   $38.05   $38.05   $38.10  
  Purchase #3 $185.31   8.339%   $200.763   $200.76   $200.75   $200.80  
  Purchase #4 $96.98   13.471%   $110.0442   $110.04   $110.05   $110.00  
  Purchase #5 $189.74   4.794%   $198.8361   $198.84   $198.85   $198.80  
  Purchase #6 $243.89   10.597%   $269.735   $269.74   $269.75   $269.70  
  Purchase #7 $5.65   6.399%   $6.0115   $6.01   $6.00   $6.00  
  7 purchase totals = $914.88       $1,000.0949   $1,000.09   $1,000.10   $1,000.10