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 $232.28   8.516%   $252.061   $252.06   $252.05   $252.10  
  Purchase #2 $25.71   6.827%   $27.4652   $27.47   $27.45   $27.50  
  Purchase #3 $203.27   9.846%   $223.284   $223.28   $223.30   $223.30  
  Purchase #4 $219.43   7.519%   $235.9289   $235.93   $235.95   $235.90  
  Purchase #5 $127.75   13.674%   $145.2185   $145.22   $145.20   $145.20  
  Purchase #6 $25.51   6.129%   $27.0735   $27.07   $27.05   $27.10  
  Purchase #7 $105.63   7.580%   $113.6368   $113.64   $113.65   $113.60  
  7 purchase totals = $939.58       $1,024.6679   $1,024.67   $1,024.65   $1,024.70