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 $89.38   10.369%   $98.6478   $98.65   $98.65   $98.60  
  Purchase #2 $169.79   7.603%   $182.6991   $182.70   $182.70   $182.70  
  Purchase #3 $153.40   11.290%   $170.7189   $170.72   $170.70   $170.70  
  Purchase #4 $28.45   10.696%   $31.493   $31.49   $31.50   $31.50  
  Purchase #5 $99.64   4.499%   $104.1228   $104.12   $104.10   $104.10  
  Purchase #6 $206.89   6.184%   $219.6841   $219.68   $219.70   $219.70  
  Purchase #7 $207.26   10.493%   $229.0078   $229.01   $229.00   $229.00  
  7 purchase totals = $954.81       $1,036.3735   $1,036.37   $1,036.35   $1,036.30