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 $174.27   8.483%   $189.0533   $189.05   $189.05   $189.10  
  Purchase #2 $53.78   13.360%   $60.965   $60.97   $60.95   $61.00  
  Purchase #3 $143.79   4.207%   $149.8392   $149.84   $149.85   $149.80  
  Purchase #4 $78.62   9.359%   $85.978   $85.98   $86.00   $86.00  
  Purchase #5 $215.86   8.651%   $234.534   $234.53   $234.55   $234.50  
  Purchase #6 $145.66   6.771%   $155.5226   $155.52   $155.50   $155.50  
  Purchase #7 $46.97   6.769%   $50.1494   $50.15   $50.15   $50.10  
  7 purchase totals = $858.95       $926.0415   $926.04   $926.05   $926.00