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 $41.57   8.198%   $44.9779   $44.98   $45.00   $45.00  
  Purchase #2 $184.79   7.597%   $198.8285   $198.83   $198.85   $198.80  
  Purchase #3 $220.99   7.498%   $237.5598   $237.56   $237.55   $237.60  
  Purchase #4 $219.41   4.603%   $229.5094   $229.51   $229.50   $229.50  
  Purchase #5 $177.35   9.753%   $194.6469   $194.65   $194.65   $194.60  
  Purchase #6 $47.27   11.373%   $52.646   $52.65   $52.65   $52.60  
  Purchase #7 $99.84   6.227%   $106.057   $106.06   $106.05   $106.10  
  7 purchase totals = $991.22       $1,064.2255   $1,064.24   $1,064.25   $1,064.20