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 $218.44   11.344%   $243.2198   $243.22   $243.20   $243.20  
  Purchase #2 $155.53   9.582%   $170.4329   $170.43   $170.45   $170.40  
  Purchase #3 $23.84   10.848%   $26.4262   $26.43   $26.45   $26.40  
  Purchase #4 $208.96   5.276%   $219.9847   $219.98   $220.00   $220.00  
  Purchase #5 $120.37   8.773%   $130.9301   $130.93   $130.95   $130.90  
  Purchase #6 $40.74   11.129%   $45.274   $45.27   $45.25   $45.30  
  Purchase #7 $216.55   4.271%   $225.7989   $225.80   $225.80   $225.80  
  7 purchase totals = $984.43       $1,062.0666   $1,062.06   $1,062.10   $1,062.00