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 $186.88   8.656%   $203.0563   $203.06   $203.05   $203.10  
  Purchase #2 $88.51   4.228%   $92.2522   $92.25   $92.25   $92.30  
  Purchase #3 $204.80   9.607%   $224.4751   $224.48   $224.50   $224.50  
  Purchase #4 $106.94   13.617%   $121.502   $121.50   $121.50   $121.50  
  Purchase #5 $173.51   4.582%   $181.4602   $181.46   $181.45   $181.50  
  Purchase #6 $59.41   12.592%   $66.8909   $66.89   $66.90   $66.90  
  Purchase #7 $124.92   11.567%   $139.3695   $139.37   $139.35   $139.40  
  7 purchase totals = $944.97       $1,029.0062   $1,029.01   $1,029.00   $1,029.20