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 $87.66   7.772%   $94.4729   $94.47   $94.45   $94.50  
  Purchase #2 $205.31   5.485%   $216.5713   $216.57   $216.55   $216.60  
  Purchase #3 $128.61   3.153%   $132.6651   $132.67   $132.65   $132.70  
  Purchase #4 $236.75   4.259%   $246.8332   $246.83   $246.85   $246.80  
  Purchase #5 $161.84   8.489%   $175.5786   $175.58   $175.60   $175.60  
  Purchase #6 $99.87   10.807%   $110.663   $110.66   $110.65   $110.70  
  Purchase #7 $40.72   8.167%   $44.0456   $44.05   $44.05   $44.00  
  7 purchase totals = $960.76       $1,020.8297   $1,020.83   $1,020.80   $1,020.90