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 $126.53   12.219%   $141.9907   $141.99   $142.00   $142.00  
  Purchase #2 $56.82   3.203%   $58.6399   $58.64   $58.65   $58.60  
  Purchase #3 $182.52   4.662%   $191.0291   $191.03   $191.05   $191.00  
  Purchase #4 $211.39   8.816%   $230.0261   $230.03   $230.05   $230.00  
  Purchase #5 $60.30   13.310%   $68.3259   $68.33   $68.35   $68.30  
  Purchase #6 $96.90   10.435%   $107.0115   $107.01   $107.00   $107.00  
  Purchase #7 $245.87   6.307%   $261.377   $261.38   $261.40   $261.40  
  7 purchase totals = $980.33       $1,058.4002   $1,058.41   $1,058.50   $1,058.30