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 $62.57   7.847%   $67.4799   $67.48   $67.50   $67.50  
  Purchase #2 $165.76   10.869%   $183.7765   $183.78   $183.80   $183.80  
  Purchase #3 $101.40   9.199%   $110.7278   $110.73   $110.75   $110.70  
  Purchase #4 $204.65   3.160%   $211.1169   $211.12   $211.10   $211.10  
  Purchase #5 $72.81   11.746%   $81.3623   $81.36   $81.35   $81.40  
  Purchase #6 $241.41   10.728%   $267.3085   $267.31   $267.30   $267.30  
  Purchase #7 $111.31   8.265%   $120.5098   $120.51   $120.50   $120.50  
  7 purchase totals = $959.91       $1,042.2817   $1,042.29   $1,042.30   $1,042.30