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 $153.80   7.113%   $164.7398   $164.74   $164.75   $164.70  
  Purchase #2 $53.49   4.689%   $55.9981   $56.00   $56.00   $56.00  
  Purchase #3 $238.98   13.112%   $270.3151   $270.32   $270.30   $270.30  
  Purchase #4 $225.85   10.278%   $249.0629   $249.06   $249.05   $249.10  
  Purchase #5 $58.44   3.372%   $60.4106   $60.41   $60.40   $60.40  
  Purchase #6 $39.69   9.453%   $43.4419   $43.44   $43.45   $43.40  
  Purchase #7 $223.80   12.179%   $251.0566   $251.06   $251.05   $251.10  
  7 purchase totals = $994.05       $1,095.0250   $1,095.03   $1,095.00   $1,095.00