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 $54.57   11.612%   $60.9067   $60.91   $60.90   $60.90  
  Purchase #2 $55.84   12.159%   $62.6296   $62.63   $62.65   $62.60  
  Purchase #3 $139.69   9.647%   $153.1659   $153.17   $153.15   $153.20  
  Purchase #4 $181.65   11.836%   $203.1501   $203.15   $203.15   $203.20  
  Purchase #5 $114.92   12.714%   $129.5309   $129.53   $129.55   $129.50  
  Purchase #6 $223.52   4.782%   $234.2087   $234.21   $234.20   $234.20  
  Purchase #7 $157.79   3.756%   $163.7166   $163.72   $163.70   $163.70  
  7 purchase totals = $927.98       $1,007.3085   $1,007.32   $1,007.30   $1,007.30