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 $62.39   6.559%   $66.4822   $66.48   $66.50   $66.50  
  Purchase #2 $41.35   11.759%   $46.2123   $46.21   $46.20   $46.20  
  Purchase #3 $84.86   11.696%   $94.7852   $94.79   $94.80   $94.80  
  Purchase #4 $134.26   5.404%   $141.5154   $141.52   $141.50   $141.50  
  Purchase #5 $232.27   6.499%   $247.3652   $247.37   $247.35   $247.40  
  Purchase #6 $130.82   12.524%   $147.2039   $147.20   $147.20   $147.20  
  Purchase #7 $178.96   5.750%   $189.2502   $189.25   $189.25   $189.30  
  7 purchase totals = $864.91       $932.8144   $932.82   $932.80   $932.90