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 $181.77   12.166%   $203.8841   $203.88   $203.90   $203.90  
  Purchase #2 $233.86   13.146%   $264.6032   $264.60   $264.60   $264.60  
  Purchase #3 $79.38   10.859%   $87.9999   $88.00   $88.00   $88.00  
  Purchase #4 $209.99   11.525%   $234.1913   $234.19   $234.20   $234.20  
  Purchase #5 $197.91   4.532%   $206.8793   $206.88   $206.90   $206.90  
  Purchase #6 $170.96   4.301%   $178.313   $178.31   $178.30   $178.30  
  Purchase #7 $69.64   9.654%   $76.363   $76.36   $76.35   $76.40  
  7 purchase totals = $1,143.51       $1,252.2338   $1,252.22   $1,252.25   $1,252.30