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 $192.53   10.598%   $212.9343   $212.93   $212.95   $212.90  
  Purchase #2 $169.69   13.562%   $192.7034   $192.70   $192.70   $192.70  
  Purchase #3 $61.59   10.656%   $68.153   $68.15   $68.15   $68.20  
  Purchase #4 $129.97   6.759%   $138.7547   $138.75   $138.75   $138.80  
  Purchase #5 $160.75   10.426%   $177.5098   $177.51   $177.50   $177.50  
  Purchase #6 $106.43   7.740%   $114.6677   $114.67   $114.65   $114.70  
  Purchase #7 $108.99   7.380%   $117.0335   $117.03   $117.05   $117.00  
  7 purchase totals = $929.95       $1,021.7564   $1,021.74   $1,021.75   $1,021.80