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 $236.59   6.818%   $252.7207   $252.72   $252.70   $252.70  
  Purchase #2 $249.77   5.507%   $263.5248   $263.52   $263.50   $263.50  
  Purchase #3 $191.52   5.485%   $202.0249   $202.02   $202.00   $202.00  
  Purchase #4 $46.40   11.107%   $51.5536   $51.55   $51.55   $51.60  
  Purchase #5 $54.58   11.512%   $60.8632   $60.86   $60.85   $60.90  
  Purchase #6 $53.96   5.555%   $56.9575   $56.96   $56.95   $57.00  
  Purchase #7 $129.50   5.464%   $136.5759   $136.58   $136.60   $136.60  
  7 purchase totals = $962.32       $1,024.2206   $1,024.21   $1,024.15   $1,024.30