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 $238.56   5.852%   $252.5205   $252.52   $252.50   $252.50  
  Purchase #2 $220.79   10.257%   $243.4364   $243.44   $243.45   $243.40  
  Purchase #3 $246.54   11.700%   $275.3852   $275.39   $275.40   $275.40  
  Purchase #4 $103.47   13.226%   $117.1549   $117.15   $117.15   $117.20  
  Purchase #5 $88.28   8.337%   $95.6399   $95.64   $95.65   $95.60  
  Purchase #6 $21.25   6.713%   $22.6765   $22.68   $22.70   $22.70  
  Purchase #7 $21.58   13.575%   $24.5095   $24.51   $24.50   $24.50  
  7 purchase totals = $940.47       $1,031.3229   $1,031.33   $1,031.35   $1,031.30