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 $96.56   10.317%   $106.5221   $106.52   $106.50   $106.50  
  Purchase #2 $120.33   12.476%   $135.3424   $135.34   $135.35   $135.30  
  Purchase #3 $248.34   10.758%   $275.0564   $275.06   $275.05   $275.10  
  Purchase #4 $156.83   3.783%   $162.7629   $162.76   $162.75   $162.80  
  Purchase #5 $26.69   9.108%   $29.1209   $29.12   $29.10   $29.10  
  Purchase #6 $165.25   10.753%   $183.0193   $183.02   $183.00   $183.00  
  Purchase #7 $201.78   12.478%   $226.9581   $226.96   $226.95   $227.00  
  7 purchase totals = $1,015.78       $1,118.7821   $1,118.78   $1,118.70   $1,118.80