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 $60.27   9.580%   $66.0439   $66.04   $66.05   $66.00  
  Purchase #2 $138.37   4.772%   $144.973   $144.97   $144.95   $145.00  
  Purchase #3 $159.81   9.346%   $174.7458   $174.75   $174.75   $174.70  
  Purchase #4 $137.30   5.618%   $145.0135   $145.01   $145.00   $145.00  
  Purchase #5 $76.45   5.499%   $80.654   $80.65   $80.65   $80.70  
  Purchase #6 $162.75   7.611%   $175.1369   $175.14   $175.15   $175.10  
  Purchase #7 $205.83   13.160%   $232.9172   $232.92   $232.90   $232.90  
  7 purchase totals = $940.78       $1,019.4843   $1,019.48   $1,019.45   $1,019.40