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 $73.61   5.825%   $77.8978   $77.90   $77.90   $77.90  
  Purchase #2 $221.93   6.573%   $236.5175   $236.52   $236.50   $236.50  
  Purchase #3 $52.41   12.534%   $58.9791   $58.98   $59.00   $59.00  
  Purchase #4 $232.96   5.600%   $246.0058   $246.01   $246.00   $246.00  
  Purchase #5 $50.42   12.671%   $56.8087   $56.81   $56.80   $56.80  
  Purchase #6 $157.29   6.135%   $166.9397   $166.94   $166.95   $166.90  
  Purchase #7 $65.79   11.868%   $73.598   $73.60   $73.60   $73.60  
  7 purchase totals = $854.41       $916.7466   $916.76   $916.75   $916.70