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 $213.66   6.706%   $227.988   $227.99   $228.00   $228.00  
  Purchase #2 $66.74   5.771%   $70.5916   $70.59   $70.60   $70.60  
  Purchase #3 $135.89   10.836%   $150.615   $150.62   $150.60   $150.60  
  Purchase #4 $184.92   10.310%   $203.9853   $203.99   $204.00   $204.00  
  Purchase #5 $14.26   6.261%   $15.1528   $15.15   $15.15   $15.20  
  Purchase #6 $199.98   10.809%   $221.5958   $221.60   $221.60   $221.60  
  Purchase #7 $154.67   7.369%   $166.0676   $166.07   $166.05   $166.10  
  7 purchase totals = $970.12       $1,055.9961   $1,056.01   $1,056.00   $1,056.10