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 $14.97   13.325%   $16.9648   $16.96   $16.95   $17.00  
  Purchase #2 $218.63   5.133%   $229.8523   $229.85   $229.85   $229.90  
  Purchase #3 $198.27   11.386%   $220.845   $220.85   $220.85   $220.80  
  Purchase #4 $55.96   5.809%   $59.2107   $59.21   $59.20   $59.20  
  Purchase #5 $184.58   7.798%   $198.9735   $198.97   $198.95   $199.00  
  Purchase #6 $57.37   5.163%   $60.332   $60.33   $60.35   $60.30  
  Purchase #7 $211.93   6.586%   $225.8877   $225.89   $225.90   $225.90  
  7 purchase totals = $941.71       $1,012.0660   $1,012.06   $1,012.05   $1,012.10