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 $43.78   13.743%   $49.7967   $49.80   $49.80   $49.80  
  Purchase #2 $7.32   8.683%   $7.9556   $7.96   $7.95   $8.00  
  Purchase #3 $86.35   9.449%   $94.5092   $94.51   $94.50   $94.50  
  Purchase #4 $174.82   13.386%   $198.2214   $198.22   $198.20   $198.20  
  Purchase #5 $113.98   4.651%   $119.2812   $119.28   $119.30   $119.30  
  Purchase #6 $192.95   13.508%   $219.0137   $219.01   $219.00   $219.00  
  Purchase #7 $92.81   3.115%   $95.701   $95.70   $95.70   $95.70  
  7 purchase totals = $712.01       $784.4788   $784.48   $784.45   $784.50