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 $201.99   5.461%   $213.0207   $213.02   $213.00   $213.00  
  Purchase #2 $56.53   12.864%   $63.802   $63.80   $63.80   $63.80  
  Purchase #3 $87.67   6.375%   $93.259   $93.26   $93.25   $93.30  
  Purchase #4 $168.69   12.685%   $190.0883   $190.09   $190.10   $190.10  
  Purchase #5 $61.85   5.191%   $65.0606   $65.06   $65.05   $65.10  
  Purchase #6 $105.55   11.488%   $117.6756   $117.68   $117.70   $117.70  
  Purchase #7 $241.52   5.717%   $255.3277   $255.33   $255.35   $255.30  
  7 purchase totals = $923.80       $998.2339   $998.24   $998.25   $998.30