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 $95.97   9.831%   $105.4048   $105.40   $105.40   $105.40  
  Purchase #2 $215.98   9.213%   $235.8782   $235.88   $235.90   $235.90  
  Purchase #3 $77.34   12.746%   $87.1978   $87.20   $87.20   $87.20  
  Purchase #4 $204.97   12.524%   $230.6404   $230.64   $230.65   $230.60  
  Purchase #5 $50.92   12.799%   $57.4373   $57.44   $57.45   $57.40  
  Purchase #6 $81.42   10.712%   $90.1417   $90.14   $90.15   $90.10  
  Purchase #7 $33.76   8.465%   $36.6178   $36.62   $36.60   $36.60  
  7 purchase totals = $760.36       $843.3180   $843.32   $843.35   $843.20