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 $54.72   3.403%   $56.5821   $56.58   $56.60   $56.60  
  Purchase #2 $6.38   3.210%   $6.5848   $6.58   $6.60   $6.60  
  Purchase #3 $40.67   7.273%   $43.6279   $43.63   $43.65   $43.60  
  Purchase #4 $235.37   12.469%   $264.7183   $264.72   $264.70   $264.70  
  Purchase #5 $213.64   5.627%   $225.6615   $225.66   $225.65   $225.70  
  Purchase #6 $192.60   13.758%   $219.0979   $219.10   $219.10   $219.10  
  Purchase #7 $120.95   7.751%   $130.3248   $130.32   $130.30   $130.30  
  7 purchase totals = $864.33       $946.5973   $946.59   $946.60   $946.60