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 $202.79   7.726%   $218.4576   $218.46   $218.45   $218.50  
  Purchase #2 $50.66   11.169%   $56.3182   $56.32   $56.30   $56.30  
  Purchase #3 $211.85   8.736%   $230.3572   $230.36   $230.35   $230.40  
  Purchase #4 $68.65   10.266%   $75.6976   $75.70   $75.70   $75.70  
  Purchase #5 $141.77   9.352%   $155.0283   $155.03   $155.05   $155.00  
  Purchase #6 $123.68   12.191%   $138.7578   $138.76   $138.75   $138.80  
  Purchase #7 $175.37   5.110%   $184.3314   $184.33   $184.35   $184.30  
  7 purchase totals = $974.77       $1,058.9481   $1,058.96   $1,058.95   $1,059.00