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 $175.55   6.284%   $186.5816   $186.58   $186.60   $186.60  
  Purchase #2 $79.88   6.359%   $84.9596   $84.96   $84.95   $85.00  
  Purchase #3 $174.30   11.165%   $193.7606   $193.76   $193.75   $193.80  
  Purchase #4 $170.98   11.316%   $190.3281   $190.33   $190.35   $190.30  
  Purchase #5 $199.93   5.761%   $211.448   $211.45   $211.45   $211.40  
  Purchase #6 $50.99   9.138%   $55.6495   $55.65   $55.65   $55.60  
  Purchase #7 $39.43   11.221%   $43.8544   $43.85   $43.85   $43.90  
  7 purchase totals = $891.06       $966.5818   $966.58   $966.60   $966.60