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 $231.82   3.152%   $239.127   $239.13   $239.15   $239.10  
  Purchase #2 $96.79   8.467%   $104.9852   $104.99   $105.00   $105.00  
  Purchase #3 $91.78   13.186%   $103.8821   $103.88   $103.90   $103.90  
  Purchase #4 $11.97   3.475%   $12.386   $12.39   $12.40   $12.40  
  Purchase #5 $232.72   4.453%   $243.083   $243.08   $243.10   $243.10  
  Purchase #6 $243.88   12.867%   $275.26   $275.26   $275.25   $275.30  
  Purchase #7 $71.41   12.700%   $80.4791   $80.48   $80.50   $80.50  
  7 purchase totals = $980.37       $1,059.2024   $1,059.21   $1,059.30   $1,059.30