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 $200.27   3.523%   $207.3255   $207.33   $207.35   $207.30  
  Purchase #2 $244.90   9.305%   $267.6879   $267.69   $267.70   $267.70  
  Purchase #3 $98.41   8.228%   $106.5072   $106.51   $106.50   $106.50  
  Purchase #4 $67.49   12.545%   $75.9566   $75.96   $75.95   $76.00  
  Purchase #5 $225.85   13.387%   $256.0845   $256.08   $256.10   $256.10  
  Purchase #6 $208.64   8.406%   $226.1783   $226.18   $226.20   $226.20  
  Purchase #7 $201.39   7.531%   $216.5567   $216.56   $216.55   $216.60  
  7 purchase totals = $1,246.95       $1,356.2967   $1,356.31   $1,356.35   $1,356.40