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 $160.84   11.410%   $179.1918   $179.19   $179.20   $179.20  
  Purchase #2 $197.96   9.794%   $217.3482   $217.35   $217.35   $217.30  
  Purchase #3 $163.37   8.574%   $177.3773   $177.38   $177.40   $177.40  
  Purchase #4 $125.62   7.704%   $135.2978   $135.30   $135.30   $135.30  
  Purchase #5 $224.62   10.148%   $247.4144   $247.41   $247.40   $247.40  
  Purchase #6 $173.78   4.608%   $181.7878   $181.79   $181.80   $181.80  
  Purchase #7 $60.32   4.592%   $63.0899   $63.09   $63.10   $63.10  
  7 purchase totals = $1,106.51       $1,201.5072   $1,201.51   $1,201.55   $1,201.50