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 $101.67   11.839%   $113.7067   $113.71   $113.70   $113.70  
  Purchase #2 $217.57   11.687%   $242.9974   $243.00   $243.00   $243.00  
  Purchase #3 $56.80   12.741%   $64.0369   $64.04   $64.05   $64.00  
  Purchase #4 $195.80   8.663%   $212.7622   $212.76   $212.75   $212.80  
  Purchase #5 $147.58   12.202%   $165.5877   $165.59   $165.60   $165.60  
  Purchase #6 $111.30   8.851%   $121.1512   $121.15   $121.15   $121.20  
  Purchase #7 $95.64   4.343%   $99.7936   $99.79   $99.80   $99.80  
  7 purchase totals = $926.36       $1,020.0357   $1,020.04   $1,020.05   $1,020.10