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 $5.49   3.844%   $5.701   $5.70   $5.70   $5.70  
  Purchase #2 $108.31   6.299%   $115.1324   $115.13   $115.15   $115.10  
  Purchase #3 $230.80   3.749%   $239.4527   $239.45   $239.45   $239.50  
  Purchase #4 $203.99   6.368%   $216.9801   $216.98   $217.00   $217.00  
  Purchase #5 $39.80   3.570%   $41.2209   $41.22   $41.20   $41.20  
  Purchase #6 $20.49   7.767%   $22.0815   $22.08   $22.10   $22.10  
  Purchase #7 $42.87   9.642%   $47.0035   $47.00   $47.00   $47.00  
  7 purchase totals = $651.75       $687.5721   $687.56   $687.60   $687.60