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 $204.55   10.808%   $226.6578   $226.66   $226.65   $226.70  
  Purchase #2 $74.98   8.610%   $81.4358   $81.44   $81.45   $81.40  
  Purchase #3 $50.79   7.757%   $54.7298   $54.73   $54.75   $54.70  
  Purchase #4 $141.50   6.556%   $150.7767   $150.78   $150.80   $150.80  
  Purchase #5 $183.74   11.367%   $204.6257   $204.63   $204.65   $204.60  
  Purchase #6 $42.42   12.605%   $47.767   $47.77   $47.75   $47.80  
  Purchase #7 $216.52   8.450%   $234.8159   $234.82   $234.80   $234.80  
  7 purchase totals = $914.50       $1,000.8087   $1,000.83   $1,000.85   $1,000.80