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 $20.36   7.471%   $21.8811   $21.88   $21.90   $21.90  
  Purchase #2 $122.28   5.204%   $128.6435   $128.64   $128.65   $128.60  
  Purchase #3 $244.46   12.580%   $275.2131   $275.21   $275.20   $275.20  
  Purchase #4 $245.84   12.292%   $276.0587   $276.06   $276.05   $276.10  
  Purchase #5 $40.56   11.458%   $45.2074   $45.21   $45.20   $45.20  
  Purchase #6 $63.37   7.651%   $68.2184   $68.22   $68.20   $68.20  
  Purchase #7 $29.64   11.435%   $33.0293   $33.03   $33.05   $33.00  
  7 purchase totals = $766.51       $848.2515   $848.25   $848.25   $848.20