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 $73.25   5.822%   $77.5146   $77.51   $77.50   $77.50  
  Purchase #2 $199.94   10.361%   $220.6558   $220.66   $220.65   $220.70  
  Purchase #3 $95.49   11.388%   $106.3644   $106.36   $106.35   $106.40  
  Purchase #4 $42.87   4.127%   $44.6392   $44.64   $44.65   $44.60  
  Purchase #5 $147.27   13.464%   $167.0984   $167.10   $167.10   $167.10  
  Purchase #6 $250.69   5.286%   $263.9415   $263.94   $263.95   $263.90  
  Purchase #7 $162.41   6.468%   $172.9147   $172.91   $172.90   $172.90  
  7 purchase totals = $971.92       $1,053.1286   $1,053.12   $1,053.10   $1,053.10