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 $173.62   7.656%   $186.9123   $186.91   $186.90   $186.90  
  Purchase #2 $188.38   7.433%   $202.3823   $202.38   $202.40   $202.40  
  Purchase #3 $66.85   3.149%   $68.9551   $68.96   $68.95   $69.00  
  Purchase #4 $130.30   7.378%   $139.9135   $139.91   $139.90   $139.90  
  Purchase #5 $202.58   3.201%   $209.0646   $209.06   $209.05   $209.10  
  Purchase #6 $115.92   5.807%   $122.6515   $122.65   $122.65   $122.70  
  Purchase #7 $78.77   4.755%   $82.5155   $82.52   $82.50   $82.50  
  7 purchase totals = $956.42       $1,012.3948   $1,012.39   $1,012.35   $1,012.50