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 $208.99   12.807%   $235.7553   $235.76   $235.75   $235.80  
  Purchase #2 $205.93   11.847%   $230.3265   $230.33   $230.35   $230.30  
  Purchase #3 $138.95   12.254%   $155.9769   $155.98   $156.00   $156.00  
  Purchase #4 $162.80   4.175%   $169.5969   $169.60   $169.60   $169.60  
  Purchase #5 $69.42   11.735%   $77.5664   $77.57   $77.55   $77.60  
  Purchase #6 $20.25   7.751%   $21.8196   $21.82   $21.80   $21.80  
  Purchase #7 $141.97   12.861%   $160.2288   $160.23   $160.25   $160.20  
  7 purchase totals = $948.31       $1,051.2704   $1,051.29   $1,051.30   $1,051.30