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 $169.39   4.741%   $177.4208   $177.42   $177.40   $177.40  
  Purchase #2 $128.94   4.180%   $134.3297   $134.33   $134.35   $134.30  
  Purchase #3 $73.93   5.418%   $77.9355   $77.94   $77.95   $77.90  
  Purchase #4 $203.51   9.830%   $223.515   $223.52   $223.50   $223.50  
  Purchase #5 $26.82   9.839%   $29.4588   $29.46   $29.45   $29.50  
  Purchase #6 $238.38   5.822%   $252.2585   $252.26   $252.25   $252.30  
  Purchase #7 $132.89   12.445%   $149.4282   $149.43   $149.45   $149.40  
  7 purchase totals = $973.86       $1,044.3465   $1,044.36   $1,044.35   $1,044.30