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 $63.51   12.219%   $71.2703   $71.27   $71.25   $71.30  
  Purchase #2 $203.88   4.262%   $212.5694   $212.57   $212.55   $212.60  
  Purchase #3 $157.34   7.329%   $168.8714   $168.87   $168.85   $168.90  
  Purchase #4 $127.92   7.383%   $137.3643   $137.36   $137.35   $137.40  
  Purchase #5 $165.56   9.711%   $181.6375   $181.64   $181.65   $181.60  
  Purchase #6 $140.50   3.224%   $145.0297   $145.03   $145.05   $145.00  
  Purchase #7 $107.65   5.254%   $113.3059   $113.31   $113.30   $113.30  
  7 purchase totals = $966.36       $1,030.0485   $1,030.05   $1,030.00   $1,030.10