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 $233.94   13.242%   $264.9183   $264.92   $264.90   $264.90  
  Purchase #2 $192.84   9.544%   $211.2446   $211.24   $211.25   $211.20  
  Purchase #3 $43.93   13.118%   $49.6927   $49.69   $49.70   $49.70  
  Purchase #4 $11.55   7.851%   $12.4568   $12.46   $12.45   $12.50  
  Purchase #5 $168.62   5.329%   $177.6058   $177.61   $177.60   $177.60  
  Purchase #6 $91.72   8.589%   $99.5978   $99.60   $99.60   $99.60  
  Purchase #7 $218.39   5.470%   $230.3359   $230.34   $230.35   $230.30  
  7 purchase totals = $960.99       $1,045.8519   $1,045.86   $1,045.85   $1,045.80