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 $85.63   9.592%   $93.8436   $93.84   $93.85   $93.80  
  Purchase #2 $228.68   6.204%   $242.8673   $242.87   $242.85   $242.90  
  Purchase #3 $87.43   7.570%   $94.0485   $94.05   $94.05   $94.00  
  Purchase #4 $18.44   4.343%   $19.2408   $19.24   $19.25   $19.20  
  Purchase #5 $216.50   11.687%   $241.8024   $241.80   $241.80   $241.80  
  Purchase #6 $165.91   11.221%   $184.5268   $184.53   $184.55   $184.50  
  Purchase #7 $17.59   9.623%   $19.2827   $19.28   $19.30   $19.30  
  7 purchase totals = $820.18       $895.6121   $895.61   $895.65   $895.50