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 $209.29   11.815%   $234.0176   $234.02   $234.00   $234.00  
  Purchase #2 $189.50   11.326%   $210.9628   $210.96   $210.95   $211.00  
  Purchase #3 $68.45   10.483%   $75.6256   $75.63   $75.65   $75.60  
  Purchase #4 $231.70   8.393%   $251.1466   $251.15   $251.15   $251.10  
  Purchase #5 $115.79   5.791%   $122.4954   $122.50   $122.50   $122.50  
  Purchase #6 $187.66   12.353%   $210.8416   $210.84   $210.85   $210.80  
  Purchase #7 $107.65   5.453%   $113.5202   $113.52   $113.50   $113.50  
  7 purchase totals = $1,110.04       $1,218.6098   $1,218.62   $1,218.60   $1,218.50