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 $174.86   8.657%   $189.9976   $190.00   $190.00   $190.00  
  Purchase #2 $117.87   4.298%   $122.9361   $122.94   $122.95   $122.90  
  Purchase #3 $75.35   7.308%   $80.8566   $80.86   $80.85   $80.90  
  Purchase #4 $21.35   13.312%   $24.1921   $24.19   $24.20   $24.20  
  Purchase #5 $121.28   4.281%   $126.472   $126.47   $126.45   $126.50  
  Purchase #6 $217.78   11.304%   $242.3979   $242.40   $242.40   $242.40  
  Purchase #7 $202.48   5.667%   $213.9545   $213.95   $213.95   $214.00  
  7 purchase totals = $930.97       $1,000.8068   $1,000.81   $1,000.80   $1,000.90