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 $250.52   9.852%   $275.2012   $275.20   $275.20   $275.20  
  Purchase #2 $113.85   4.274%   $118.7159   $118.72   $118.70   $118.70  
  Purchase #3 $118.94   13.638%   $135.161   $135.16   $135.15   $135.20  
  Purchase #4 $71.60   3.364%   $74.0086   $74.01   $74.00   $74.00  
  Purchase #5 $153.65   13.493%   $174.382   $174.38   $174.40   $174.40  
  Purchase #6 $38.52   4.167%   $40.1251   $40.13   $40.15   $40.10  
  Purchase #7 $161.98   13.243%   $183.431   $183.43   $183.45   $183.40  
  7 purchase totals = $909.06       $1,001.0248   $1,001.03   $1,001.05   $1,001.00