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 $130.92   10.609%   $144.8093   $144.81   $144.80   $144.80  
  Purchase #2 $125.70   11.242%   $139.8312   $139.83   $139.85   $139.80  
  Purchase #3 $58.94   9.687%   $64.6495   $64.65   $64.65   $64.60  
  Purchase #4 $155.26   6.845%   $165.8875   $165.89   $165.90   $165.90  
  Purchase #5 $171.84   6.253%   $182.5852   $182.59   $182.60   $182.60  
  Purchase #6 $122.81   11.343%   $136.7403   $136.74   $136.75   $136.70  
  Purchase #7 $183.79   9.713%   $201.6415   $201.64   $201.65   $201.60  
  7 purchase totals = $949.26       $1,036.1445   $1,036.15   $1,036.20   $1,036.00