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 $44.83   13.265%   $50.7767   $50.78   $50.80   $50.80  
  Purchase #2 $238.56   5.247%   $251.0772   $251.08   $251.10   $251.10  
  Purchase #3 $110.86   6.663%   $118.2466   $118.25   $118.25   $118.20  
  Purchase #4 $94.64   8.196%   $102.3967   $102.40   $102.40   $102.40  
  Purchase #5 $129.87   6.443%   $138.2375   $138.24   $138.25   $138.20  
  Purchase #6 $218.98   3.761%   $227.2158   $227.22   $227.20   $227.20  
  Purchase #7 $165.58   8.690%   $179.9689   $179.97   $179.95   $180.00  
  7 purchase totals = $1,003.32       $1,067.9194   $1,067.94   $1,067.95   $1,067.90