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 $101.91   6.521%   $108.5556   $108.56   $108.55   $108.60  
  Purchase #2 $106.55   4.519%   $111.365   $111.37   $111.35   $111.40  
  Purchase #3 $52.46   8.791%   $57.0718   $57.07   $57.05   $57.10  
  Purchase #4 $239.91   9.239%   $262.0753   $262.08   $262.10   $262.10  
  Purchase #5 $60.94   12.532%   $68.577   $68.58   $68.60   $68.60  
  Purchase #6 $148.37   8.801%   $161.428   $161.43   $161.45   $161.40  
  Purchase #7 $145.31   12.578%   $163.5871   $163.59   $163.60   $163.60  
  7 purchase totals = $855.45       $932.6598   $932.68   $932.70   $932.80