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 $122.96   3.272%   $126.9833   $126.98   $127.00   $127.00  
  Purchase #2 $17.45   9.382%   $19.0872   $19.09   $19.10   $19.10  
  Purchase #3 $116.57   7.704%   $125.5506   $125.55   $125.55   $125.60  
  Purchase #4 $190.37   11.223%   $211.7352   $211.74   $211.75   $211.70  
  Purchase #5 $72.38   4.459%   $75.6074   $75.61   $75.60   $75.60  
  Purchase #6 $22.30   7.587%   $23.9919   $23.99   $24.00   $24.00  
  Purchase #7 $201.89   13.210%   $228.5597   $228.56   $228.55   $228.60  
  7 purchase totals = $743.92       $811.5153   $811.52   $811.55   $811.60