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 $92.48   11.332%   $102.9598   $102.96   $102.95   $103.00  
  Purchase #2 $40.70   12.835%   $45.9238   $45.92   $45.90   $45.90  
  Purchase #3 $72.74   11.679%   $81.2353   $81.24   $81.25   $81.20  
  Purchase #4 $243.44   10.106%   $268.042   $268.04   $268.05   $268.00  
  Purchase #5 $114.98   9.463%   $125.8606   $125.86   $125.85   $125.90  
  Purchase #6 $184.92   8.436%   $200.5199   $200.52   $200.50   $200.50  
  Purchase #7 $174.36   4.109%   $181.5245   $181.52   $181.50   $181.50  
  7 purchase totals = $923.62       $1,006.0659   $1,006.06   $1,006.00   $1,006.00