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 $7.26   9.612%   $7.9578   $7.96   $7.95   $8.00  
  Purchase #2 $50.86   11.382%   $56.6489   $56.65   $56.65   $56.60  
  Purchase #3 $199.78   11.633%   $223.0204   $223.02   $223.00   $223.00  
  Purchase #4 $88.52   8.822%   $96.3292   $96.33   $96.35   $96.30  
  Purchase #5 $171.87   13.668%   $195.3612   $195.36   $195.35   $195.40  
  Purchase #6 $175.37   9.636%   $192.2687   $192.27   $192.25   $192.30  
  Purchase #7 $152.40   12.366%   $171.2458   $171.25   $171.25   $171.20  
  7 purchase totals = $846.06       $942.8320   $942.84   $942.80   $942.80