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 $212.26   10.842%   $235.2732   $235.27   $235.25   $235.30  
  Purchase #2 $75.95   6.260%   $80.7045   $80.70   $80.70   $80.70  
  Purchase #3 $210.38   10.406%   $232.2721   $232.27   $232.25   $232.30  
  Purchase #4 $48.70   13.656%   $55.3505   $55.35   $55.35   $55.40  
  Purchase #5 $126.84   9.293%   $138.6272   $138.63   $138.65   $138.60  
  Purchase #6 $24.83   3.467%   $25.6909   $25.69   $25.70   $25.70  
  Purchase #7 $242.64   10.246%   $267.5009   $267.50   $267.50   $267.50  
  7 purchase totals = $941.60       $1,035.4193   $1,035.41   $1,035.40   $1,035.50