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 $7.32   8.627%   $7.9515   $7.95   $7.95   $8.00  
  Purchase #2 $192.78   7.121%   $206.5079   $206.51   $206.50   $206.50  
  Purchase #3 $95.64   3.288%   $98.7846   $98.78   $98.80   $98.80  
  Purchase #4 $54.29   11.744%   $60.6658   $60.67   $60.65   $60.70  
  Purchase #5 $127.27   9.674%   $139.5821   $139.58   $139.60   $139.60  
  Purchase #6 $70.86   11.194%   $78.7921   $78.79   $78.80   $78.80  
  Purchase #7 $210.88   8.280%   $228.3409   $228.34   $228.35   $228.30  
  7 purchase totals = $759.04       $820.6249   $820.62   $820.65   $820.70