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 $64.36   10.281%   $70.9769   $70.98   $71.00   $71.00  
  Purchase #2 $148.97   11.295%   $165.7962   $165.80   $165.80   $165.80  
  Purchase #3 $173.38   7.490%   $186.3662   $186.37   $186.35   $186.40  
  Purchase #4 $183.36   3.567%   $189.9005   $189.90   $189.90   $189.90  
  Purchase #5 $44.71   10.651%   $49.4721   $49.47   $49.45   $49.50  
  Purchase #6 $61.78   3.303%   $63.8206   $63.82   $63.80   $63.80  
  Purchase #7 $107.80   11.326%   $120.0094   $120.01   $120.00   $120.00  
  7 purchase totals = $784.36       $846.3419   $846.35   $846.30   $846.40