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 $227.75   8.755%   $247.6895   $247.69   $247.70   $247.70  
  Purchase #2 $14.93   9.708%   $16.3794   $16.38   $16.40   $16.40  
  Purchase #3 $57.60   4.340%   $60.0998   $60.10   $60.10   $60.10  
  Purchase #4 $71.85   13.671%   $81.6726   $81.67   $81.65   $81.70  
  Purchase #5 $161.97   5.700%   $171.2023   $171.20   $171.20   $171.20  
  Purchase #6 $206.52   5.692%   $218.2751   $218.28   $218.30   $218.30  
  Purchase #7 $234.79   6.406%   $249.8306   $249.83   $249.85   $249.80  
  7 purchase totals = $975.41       $1,045.1493   $1,045.15   $1,045.20   $1,045.20